spi: npcm-fiu: add NPCM7xx FIU controller driver

Add Nuvoton NPCM BMC Flash Interface Unit(FIU) SPI master
controller driver using SPI-MEM interface.

The FIU supports single, dual or quad communication interface.
The FIU controller driver provides flash access in UMA(User
Mode Access) mode by using an indirect address/data mechanism.

the dts node is followed upstream kernel dts name.

Signed-off-by: Jim Liu <JJLIU0@nuvoton.com>
Signed-off-by: Stanley Chu <yschu@nuvoton.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
[Jagan: fixed the Kconfig, Makefile order]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>