drivers: memc: fix XIP active logic for RT6xx/RT5xx

memc driver was setup to always assume the flexSPI would be in XIP mode,
and skip init. This is only true for the active flexSPI, which is
typically FlexSPI1. Fix this check to only skip init for FlexSPI1

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