spi: nxp_fspi: Use second last LUT entry for AHB read

spi: nxp_fspi: Use second last LUT entry for AHB read

Use a dedicated LUT (second last) for AHB read command, so we can
directly read from the AHB memory-mapped address and booting M core
for XIP on Flexspi NOR.

Signed-off-by: Ye Li <ye.li@nxp.com>