drm/vc4: Enable VC4 modules, and increase CMA size with overlay

If using the overlay, be careful not to boot to GUI or run startx,
or the Pi will almost hang, reporting stalls in kernel threads.

arch/arm/boot/dts/overlays/README

@@ -691,6 +691,14 @@ Params: txd1_pin                 GPIO pin for TXD1 (14, 32 or 40 - default 14)
         rxd1_pin                 GPIO pin for RXD1 (15, 33 or 41 - default 15)
 
 
+Name:   vc4-kms-v3d
+Info:   Enable Eric Anholt's DRM VC4 HDMI/HVS/V3D driver. Running startx or
+        booting to GUI while this overlay is in use will cause interesting
+        lockups.
+Load:   dtoverlay=vc4-kms-v3d
+Params: <None>
+
+
 Name:   vga666
 Info:   Overlay for the Fen Logic VGA666 board
         This uses GPIOs 2-21 (so no I2C), and activates the output 2-3 seconds

arch/arm/boot/dts/overlays/vc4-kms-v3d-overlay.dts

@@ -85,4 +85,11 @@
 			};
 		};
 	};
+
+	fragment@4 {
+		target-path = "/chosen";
+		__overlay__ {
+			bootargs = "cma=0x4000000";
+		};
+	};
 };

arch/arm/configs/bcm2709_defconfig

@@ -805,6 +805,8 @@ CONFIG_VIDEO_TW9903=m
 CONFIG_VIDEO_TW9906=m
 CONFIG_VIDEO_OV7640=m
 CONFIG_VIDEO_MT9V011=m
+CONFIG_DRM=m
+CONFIG_DRM_VC4=m
 CONFIG_FB=y
 CONFIG_FB_BCM2708=y
 CONFIG_FB_UDL=m

arch/arm/configs/bcmrpi_defconfig

@@ -798,6 +798,8 @@ CONFIG_VIDEO_TW9903=m
 CONFIG_VIDEO_TW9906=m
 CONFIG_VIDEO_OV7640=m
 CONFIG_VIDEO_MT9V011=m
+CONFIG_DRM=m
+CONFIG_DRM_VC4=m
 CONFIG_FB=y
 CONFIG_FB_BCM2708=y
 CONFIG_FB_UDL=m