OMAP : SPI : use devm_* functions

The various devm_* functions allocate memory that is released when a driver
detaches. This patch uses devm_request_and_ioremap
to request memory in probe function. Since the freeing is not
needed the calls are deleted from remove function.Also use
use devm_kzalloc for the cs memory allocation.

Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>