ARM: omap: Remove unused arch/arm/cpu/armv7/omap3/mem.c

These functions have been merged into the common GPMC init code
with this commit a0a37183 (ARM: omap: merge GPMC initialization code
for all platform). The file is not compiled any more. So remove it
as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Pekon Gupta <pekon@ti.com>
Cc: Tom Rini <trini@ti.com>
Acked-by: Pekon Gupta <pekon@ti.com>