spi: ca_sflash: Add CAxxxx SPI Flash Controller

Add SPI Flash controller driver for Cortina Access
CAxxxx SoCs

Signed-off-by: Pengpeng Chen <pengpeng.chen@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>
CC: Vignesh R <vigneshr@ti.com>
CC: Tom Rini <trini@konsulko.com>
[jagan: rebase on master]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>