video: Add Aeroflex Gaisler GRVGA framebuffer device driver

This patch adds support for the GRVGA framebuffer IP core from Aeroflex Gaisler.
The device is used in LEON SPARCV8 based System on Chips. Documentation can
be found here: www.gaisler.com/products/grlib/grip.pdf.

Signed-off-by: Kristoffer Glembo <kristoffer@gaisler.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>