drivers: memc: don't relocate MEMC functions unless CONFIG_FLASH=y

Only relocate memc driver when CONFIG_FLASH=y.
CONFIG_FLASH_MCUX_FLEXSPI_XIP previously was dependent on
CONFIG_FLASH, but the scope of this Kconfig has changed.

Due to this, the memc driver now must have two checks, as it should not
relocated when the driver is being used for a memory controller that does
not expose the flash driver interface.

Since the NXP HAL also relocates the underlying FlexSPI driver
using a similar check, it is updated in this commit as well.

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