spi: spi-nxp-fspi: Implement errata workaround for LS1028A

Errata ERR050568 description says that "Flash access by FlexSPI AHB
command may not work with platform frequency equal to 300 MHz" on
LS1028A.

By default, smaller length reads(equal to RX FIFO size) are done by IP
bus and larger length reads using AHB bus. For adding errata workaround,
use IP bus to read entire flash contents and disable AHB path when
platform frequency is 300Mhz.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Link: https://lore.kernel.org/r/20210302124936.1972546-5-kuldeep.singh@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>