MLK-11936: mtd: fsl-quadspi: add the DDR quad read support for Spansion NOR

MLK-11936: mtd: fsl-quadspi: add the DDR quad read support for Spansion NOR

Add the DDR quad read support for the fsl-quadspi driver.

Check the "spi-nor,ddr-quad-read-dummy" DT property, if the DT node is exit,
it means we could enable the DDR quad read.

 (1) Test this patch with imx6sx-sdb board (Spansion s25fl128s)
     The clock rate is 66MHz.

 (2) The information of NOR flash:
     -----------------------------------------------
     root@imx6qdlsolo:~# mtdinfo /dev/mtd0
     mtd0
     Name:                           21e4000.qspi
     Type:                           nor
     Eraseblock size:                65536 bytes, 64.0 KiB
     Amount of eraseblocks:          256 (16777216 bytes, 16.0 MiB)
     Minimum input/output unit size: 1 byte
     Sub-page size:                  1 byte
     Character device major/minor:   90:0
     Bad blocks are allowed:         false
     Device is writable:             true
     -----------------------------------------------

 (3) Test this patch set with UBIFS & bonnie++:
     -----------------------------------------------
	ubiattach /dev/ubi_ctrl -m 0
	ubimkvol /dev/ubi0 -N test -m
	mount -t ubifs ubi0:test tmp
	bonnie++ -d tmp -u 0 -s 10 -r 5
     -----------------------------------------------

 (4) Test this patch with mtd_speedtest.ko

     root@imx6qdlsolo:~# insmod mtd_speedtest.ko dev=0
     =================================================
     mtd_speedtest: MTD device: 0
     mtd_speedtest: not NAND flash, assume page size is 512 bytes.
     mtd_speedtest: MTD device size 16777216, eraseblock size 65536, page size 512,
                    count of eraseblocks 256, pages per eraseblock 128, OOB size 0
     mtd_speedtest: testing eraseblock write speed
     mtd_speedtest: eraseblock write speed is 665 KiB/s
     mtd_speedtest: testing eraseblock read speed
     mtd_speedtest: eraseblock read speed is 49799 KiB/s
     mtd_speedtest: testing page write speed
     mtd_speedtest: page write speed is 662 KiB/s
     mtd_speedtest: testing page read speed
     mtd_speedtest: page read speed is 24236 KiB/s
     mtd_speedtest: testing 2 page write speed
     mtd_speedtest: 2 page write speed is 657 KiB/s
     mtd_speedtest: testing 2 page read speed
     mtd_speedtest: 2 page read speed is 32637 KiB/s
     mtd_speedtest: Testing erase speed
     mtd_speedtest: erase speed is 518 KiB/s
     mtd_speedtest: Testing 2x multi-block erase speed
     mtd_speedtest: 2x multi-block erase speed is 506 KiB/s
     mtd_speedtest: Testing 4x multi-block erase speed
     mtd_speedtest: 4x multi-block erase speed is 503 KiB/s
     mtd_speedtest: Testing 8x multi-block erase speed
     mtd_speedtest: 8x multi-block erase speed is 501 KiB/s
     mtd_speedtest: Testing 16x multi-block erase speed
     mtd_speedtest: 16x multi-block erase speed is 498 KiB/s
     mtd_speedtest: Testing 32x multi-block erase speed
     mtd_speedtest: 32x multi-block erase speed is 496 KiB/s
     mtd_speedtest: Testing 64x multi-block erase speed
     mtd_speedtest: 64x multi-block erase speed is 495 KiB/s
     mtd_speedtest: finished
     =================================================

  (5) Conclusion:
     The DDR quad read could be 49799 KiB/s.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Han Xu <b45815@freescale.com>