video: vt8500: Correct descriptions in video/Kconfig

This patch corrects the descriptions for the VIA VT8500 and
Wondermedia WM8xxx-series framebuffer drivers to correctly reflect
which hardware they support.

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>