drm/vmwgfx: Add an option to change assumed FB bpp

Offer an option for advanced users who want larger modes at 16bpp.

This becomes necessary after the fix: "Work around mode set
failure in 2D VMs."  Without this patch, there would be no way
for existing advanced users to get to a high res mode, and the
regression is they will likely get a black screen after a software
update on their current VM.

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Cc: <stable@vger.kernel.org>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
index 1980e2a..89fb194 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
@@ -386,6 +386,7 @@
 	spinlock_t hw_lock;
 	spinlock_t cap_lock;
 	bool has_dx;
+	bool assume_16bpp;
 
 	/*
 	 * VGA registers.