drm/cirrus: add create_handle support.

Add create_handle support to cirrus fb. Without this, screenshot tool
in chromium OS can't work.
Signed-off-by: Lepton Wu <ytht.net@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20171108185537.56167-1-ytht.net@gmail.comSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/cirrus/cirrus_main.c

@@ -13,6 +13,14 @@
 
 #include "cirrus_drv.h"
 
+static int cirrus_create_handle(struct drm_framebuffer *fb,
+				struct drm_file* file_priv,
+				unsigned int* handle)
+{
+	struct cirrus_framebuffer *cirrus_fb = to_cirrus_framebuffer(fb);
+
+	return drm_gem_handle_create(file_priv, cirrus_fb->obj, handle);
+}
 
 static void cirrus_user_framebuffer_destroy(struct drm_framebuffer *fb)
 {
@@ -24,6 +32,7 @@ static void cirrus_user_framebuffer_destroy(struct drm_framebuffer *fb)
 }
 
 static const struct drm_framebuffer_funcs cirrus_fb_funcs = {
+	.create_handle = cirrus_create_handle,
 	.destroy = cirrus_user_framebuffer_destroy,
 };