DRM: Armada: Add Armada DRM driver

This patch adds support for the pair of LCD controllers on the Marvell
Armada 510 SoCs.  This driver supports:
- multiple contiguous scanout buffers for video and graphics
- shm backed cacheable buffer objects for X pixmaps for Vivante GPU
  acceleration
- dual lcd0 and lcd1 crt operation
- video overlay on each LCD crt via DRM planes
- page flipping of the main scanout buffers
- DRM prime for buffer export/import

This driver is trivial to extend to other Armada SoCs.

Included in this commit is the core driver with no output support; output
support is platform and encoder driver dependent.

Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/drm/drm_crtc.h

@@ -1135,4 +1135,21 @@ extern int drm_format_horz_chroma_subsampling(uint32_t format);
 extern int drm_format_vert_chroma_subsampling(uint32_t format);
 extern const char *drm_get_format_name(uint32_t format);
 
+/* Helpers */
+static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
+	uint32_t id)
+{
+	struct drm_mode_object *mo;
+	mo = drm_mode_object_find(dev, id, DRM_MODE_OBJECT_CRTC);
+	return mo ? obj_to_crtc(mo) : NULL;
+}
+
+static inline struct drm_encoder *drm_encoder_find(struct drm_device *dev,
+	uint32_t id)
+{
+	struct drm_mode_object *mo;
+	mo = drm_mode_object_find(dev, id, DRM_MODE_OBJECT_ENCODER);
+	return mo ? obj_to_encoder(mo) : NULL;
+}
+
 #endif /* __DRM_CRTC_H__ */