omap: rx51: mark reserved memory earlier

So that omap_vram_set_sdram_vram() is called before
omap_vram_reserve_sdram_memblock().

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>