ARM: omap/fb: move get_fbmem_region() to .init.text

get_fbmem_region() is only called by omapfb_reserve_sdram_memblock() and
omapfb_reserve_sram() that both live in .init.text.  So get_fbmem_region
can go there, too.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>