uboot-imx

spi: mxs: Introduce spi_cs_is_valid()

Introduce spi_cs_is_valid() for validating spi bus and chip select numbers.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>