spi: cadence-qspi: Use PHY for DAC reads if possible

Check if a read is eligible for PHY and if it is, enable PHY and DQS.

Since PHY reads only work at an address that is 16-byte aligned and of
size that is a multiple of 16 bytes, read the starting and ending
unaligned portions without PHY, and only enable PHY for the middle part.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>