glamor: Can work at depth >= 15 with current xserver Git master

(Ported from amdgpu commit 0734cdf544ffd3f2ac8749ad0e4bf43f8a5cea50)

src/radeon_bo_helper.c

@@ -39,6 +39,8 @@ radeon_get_gbm_format(int depth, int bitsPerPixel)
     case 8:
 	return GBM_FORMAT_R8;
 #endif
+    case 15:
+	return GBM_FORMAT_ARGB1555;
     case 16:
 	return GBM_FORMAT_RGB565;
     case 32:

src/radeon_glamor.c

@@ -109,9 +109,14 @@ radeon_glamor_pre_init(ScrnInfoPtr scrn)
 			   "glamor may not work (well) with GPUs < RV515.\n");
 	}
 
+#if XORG_VERSION_CURRENT < XORG_VERSION_NUMERIC(1,20,99,0,0)
 	if (scrn->depth < 24) {
+#else
+	if (scrn->depth < 15) {
+#endif
 		xf86DrvMsg(scrn->scrnIndex, s ? X_ERROR : X_WARNING,
-			   "glamor requires depth >= 24, disabling.\n");
+			   "Depth %d not supported with glamor, disabling\n",
+			   scrn->depth);
 		return FALSE;
 	}