cadence_qspi: fix odd byte read issue in STIG mode

cadence_qspi: fix odd byte read issue in STIG mode

In DDR mode, even bytes are read using DMA, while the remaining odd
bytes are read using STIG mode. However, the data is not correctly
transferred into the flash read data lower register because the
supplementary byte of the STIG opcode is not being written to the
opcode extension register, resulting in incorrect data being read.

To resolve this issue, when using STIG transactions, the corresponding
supplementary byte of any STIG opcode must be defined in the Opcode
Extension Register (Lower). Issue has been observed on the Macronix
MX66UM2G45G flashes.

Signed-off-by: Prasad Kummari <prasad.kummari@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20250702053953.640046-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>