uio: uio_pruss: replace private SRAM API with genalloc

Remove the use of the private DaVinci SRAM API in favor
of genalloc. The pool to be used is provided by platform
data.

Signed-off-by: Matt Porter <mporter@ti.com>
Signed-off-by: "Hans J. Koch" <hjk@hansjkoch.de>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>