video: vt8500: Make wmt_ge_rops optional

wmt_ge_rops is a seperate driver to vt8500/wm8505 framebuffer
driver but is currently a required option. This patch makes
accelerated raster ops optional.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Reviewed-by: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>