MLK-11941: mtd: spi-nor: add DDR quad read support

MLK-11941: mtd: spi-nor: add DDR quad read support

This patch adds the DDR quad read support by the following:

[1] add SPI_NOR_DDR_QUAD read mode.

[2] add DDR Quad read opcodes:
    SPINOR_OP_READ_1_4_4_D / SPINOR_OP_READ4_1_4_4_D

[3] add set_ddr_quad_mode() to initialize for the DDR quad read.
    Currently it only works for Spansion NOR.

[3] about the dummy cycles.
    We set the dummy with 8 for DDR quad read by default.
    The m25p80.c can not support the DDR quad read, but the SPI NOR controller
    can set the dummy value in its child DT node, and the SPI NOR framework
    can parse it out.

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