spi: npcm-fiu: add regulator feature and remove set clock

NPCM7xx/NPCM8xx default is boot from flash.
removed set clock feature due to reliability and security.
the clock will set by bootblock or tip.

Signed-off-by: Jim Liu <JJLIU0@nuvoton.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>