ARM: davinci: add platform hook to fetch the SRAM pool

Adds sram_get_gen_pool() which allows platform code to get
the machine's SRAM gen_pool. The gen_pool may be passed in
platform data for driver genalloc use.

Signed-off-by: Matt Porter <mporter@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>