powerpc/ps3: Replace the flip_ctl logic in ps3av and ps3fb by a mutex

Introduce ps3_gpu_mutex to synchronizes GPU-related operations, like:
  - invoking the L1GPU_CONTEXT_ATTRIBUTE_FB_BLIT command using the
    lv1_gpu_context_attribute() hypervisor call,
  - handling the PS3AV_CID_AVB_PARAM packet in the PS3 A/V Settings driver.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/ps3/setup.c

@@ -42,6 +42,10 @@
 #define DBG pr_debug
 #endif
 
+/* mutex synchronizing GPU accesses and video mode changes */
+DEFINE_MUTEX(ps3_gpu_mutex);
+EXPORT_SYMBOL_GPL(ps3_gpu_mutex);
+
 #if !defined(CONFIG_SMP)
 static void smp_send_stop(void) {}
 #endif