drm/armada: mark symbols static where possible

We get 2 warnings when building kernel with W=1:
drivers/gpu/drm/armada/armada_gem.c:215:27: warning: no previous prototype for 'armada_gem_alloc_object' [-Wmissing-prototypes]
drivers/gpu/drm/armada/armada_gem.c:423:1: warning: no previous prototype for 'armada_gem_prime_map_dma_buf' [-Wmissing-prototypes]

In fact, both functions are only used in the file in which they are
declared and don't need a declaration, but can be made static.
So this patch marks these functions with 'static'.

Signed-off-by: Baoyou Xie <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

drivers/gpu/drm/armada/armada_gem.c

···
 	return obj;
 }
 
-struct armada_gem_object *armada_gem_alloc_object(struct drm_device *dev,
+static struct armada_gem_object *armada_gem_alloc_object(struct drm_device *dev,
 	size_t size)
 {
 	struct armada_gem_object *obj;
···
 }
 
 /* Prime support */
-struct sg_table *
+static struct sg_table *
 armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach,
 	enum dma_data_direction dir)
 {