drm/v3d: Add support for V3D v4.2.

No compatible string for it yet, just the version-dependent changes.
They've now tied the hub and the core interrupt lines into a single
interrupt line coming out of the block.  It also turns out I made a
mistake in modeling the V3D v3.3 and v4.1 bridge as a part of V3D
itself -- the bridge is going away in favor of an external reset
controller in a larger HW module.

v2: Use consistent checks for whether we're on 4.2, and fix a leak in
    an error path.
v3: Use more general means of determining if the current 4.2 changes
    are in place, as apparently other platforms may switch back (noted
    by Dave).  Update the binding doc.
v4: Improve error handling for IRQ init.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308174336.7866-2-eric@anholt.net
Reviewed-by: Dave Emett <david.emett@broadcom.com>

drivers/gpu/drm/v3d/v3d_gem.c

@@ -6,6 +6,7 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/device.h>
 #include <linux/io.h>
 #include <linux/sched/signal.h>
@@ -70,7 +71,7 @@ v3d_idle_gca(struct v3d_dev *v3d)
 }
 
 static void
-v3d_reset_v3d(struct v3d_dev *v3d)
+v3d_reset_by_bridge(struct v3d_dev *v3d)
 {
 	int version = V3D_BRIDGE_READ(V3D_TOP_GR_BRIDGE_REVISION);
 
@@ -90,6 +91,15 @@ v3d_reset_v3d(struct v3d_dev *v3d)
 				 V3D_TOP_GR_BRIDGE_SW_INIT_1_V3D_CLK_108_SW_INIT);
 		V3D_BRIDGE_WRITE(V3D_TOP_GR_BRIDGE_SW_INIT_1, 0);
 	}
+}
+
+static void
+v3d_reset_v3d(struct v3d_dev *v3d)
+{
+	if (v3d->reset)
+		reset_control_reset(v3d->reset);
+	else
+		v3d_reset_by_bridge(v3d);
 
 	v3d_init_hw_state(v3d);
 }