drivers: spi: npcx: add SPI support to access the SPI flash

The FIU/UMA module in the NPCX chip provides an dedicated SPI interface
to access the SPI flash. This commit adds the driver support for it.
With this commit, the application can call the flash APIs
(via spi_nor.c) to access the internal flash of NPCX EC chips.

Signed-off-by: Jun Lin <CHLin56@nuvoton.com>
Change-Id: I32bbf09f6e014b728ff8e4692e48151ae759e188
15 files changed