MAINTAINERS: add separate entry for DRM TTM v2

AMD is the major user of TTM, so it also makes sense that we maintain
it.

v2: mention Alex git tree as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

MAINTAINERS

@@ -4805,6 +4805,15 @@ S:	Maintained
 F:	drivers/gpu/drm/tinydrm/
 F:	include/drm/tinydrm/
 
+DRM TTM SUBSYSTEM
+M:	Christian Koenig <christian.koenig@amd.com>
+M:	Roger He <Hongbo.He@amd.com>
+T:	git git://people.freedesktop.org/~agd5f/linux
+S:	Maintained
+L:	dri-devel@lists.freedesktop.org
+F:	include/drm/ttm/
+F:	drivers/gpu/drm/ttm/
+
 DSBR100 USB FM RADIO DRIVER
 M:	Alexey Klimov <klimov.linux@gmail.com>
 L:	linux-media@vger.kernel.org