driver: flash: mcux_flexspi_nor: Fix for is25lpxxxd chips

IS25LPXXXD uses the same jedec-id as IS25LPXXX, but the latter has
an extended read register, similar to IS25WPXXX. This change will
attempt to read the extended read register to determine what the
appropriate initialization value for read register should be.

Signed-off-by: John Barbero Unenge <git@lsrkttn.com>