mtd: spi-nor: add driver for NXP SPI Flash Interface (SPIFI)

Add SPI-NOR driver for the SPI Flash Interface (SPIFI)
controller that is found on newer NXP MCU devices.

The controller supports serial SPI Flash devices with 1-, 2-
and 4-bit width in either SPI mode 0 or 3. The controller
can operate in either command or memory mode. In memory mode
the Flash is exposed as normal memory and can be directly
accessed by the CPU.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>