drm/msm: don't crash if no msm.vram param

If VRAM carveout is used, due to no IOMMU, we should have a default
value for msm.vram so that we don't simply crash.

Reported-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_drv.c

@@ -52,7 +52,7 @@ module_param(reglog, bool, 0600);
 #define reglog 0
 #endif
 
-static char *vram;
+static char *vram = "16m";
 MODULE_PARM_DESC(vram, "Configure VRAM size (for devices without IOMMU/GPUMMU");
 module_param(vram, charp, 0);