arch/arm/mach-davinci/sram.c: use gen_pool_dma_alloc() to sram.c

Since gen_pool_dma_alloc() is introduced, we implement it to simplify code.

Signed-off-by: Nicolin Chen <b42378@freescale.com>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>