spi_qsd: Add support for pinctrl to configure chip select pins

As part of pinctrl frame work migration, add support
for chip select GPIO configuration using pinctrl frame work.

Now SPI driver supports both pinctrl frame work as
well as GPIO mux to configure chip select GPIO's.

CRs-Fixed: 621109
Change-Id: Id4aa58f9e2d2ae667719c6c600fb35b88b0f5b77
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>