MAINTAINERS: Add myself for the new VC4 (RPi GPU) graphics driver.

Signed-off-by: Eric Anholt <eric@anholt.net>
[Emil Velikov: drop wildcard, add UAPI and Documentation files]
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462283659-1314-1-git-send-email-emil.l.velikov@gmail.com