drm/nouveau: make vbios parser runnable from an atomic context

The nv50 display isr bh needs to be converted to a tasklet, which means
we can't sleep anymore.  The places we execute vbios init tables are
rare, and not in any way performance critical, so this isn't a huge
problem.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_bios.h b/drivers/gpu/drm/nouveau/nouveau_bios.h
index 50a648e..8a54fa7 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bios.h
+++ b/drivers/gpu/drm/nouveau/nouveau_bios.h
@@ -251,7 +251,7 @@
 	uint8_t digital_min_front_porch;
 	bool fp_no_ddc;
 
-	struct mutex lock;
+	spinlock_t lock;
 
 	uint8_t data[NV_PROM_SIZE];
 	unsigned int length;