drivers: flash: flash_mcux_flexspi_nor: better handle legacy SFDP tables

Implement more robust handling for legacy SFDP tables, which may not
implement some of the JEDEC defined DWORDS for SFDP data. Instead of
failing to probe/initialize the flash when these DWORDS are not defined
in the basic flash parameter table, revert to sane defaults for SPI
flash.

Fixes #72051

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>