ARM: OMAP: SRAM: resolve sparse warnings

Commit bb772094 ("ARM: OMAP: Move
omap2+ specific parts of sram.c to mach-omap2") adds some new sparse
warnings:

arch/arm/plat-omap/sram.c:43:6: warning: symbol 'omap_sram_push_address' was not declared. Should it be static?
arch/arm/plat-omap/sram.c:65:6: warning: symbol 'omap_sram_reset' was not declared. Should it be static?
arch/arm/plat-omap/sram.c:73:13: warning: symbol 'omap_map_sram' was not declared. Should it be static?

This second version fixes the warnings by including <plat/sram.h>, at
Tony's request.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Tony Lindgren <tony@atomide.com>