MLK-16769-1: clk: imx7d: create clocks behind rawnand clock gate

MLK-16769-1: clk: imx7d: create clocks behind rawnand clock gate

Merge community clock code change for i.MX7D.

The rawnand clock gate gates two clocks, NAND_USDHC_BUS_CLK_ROOT
and NAND_CLK_ROOT. However, the gate has been in the chain of the
latter only. This does not allow to use the NAND_USDHC_BUS_CLK_ROOT
only, e.g. as required by APBH-Bridge-DMA.

Add new clocks which represent the clock after the gate, and use a
shared clock gate to correctly model the hardware.

Signed-off-by: Han Xu <han.xu@nxp.com>