svga: create BGRX render target view for BGRX_UNORM surface

svga: create BGRX render target view for BGRX_UNORM surface

Currently we adjust the view format when we are asked to create a
BGRA render target view for BGRX surface. But we only look for
SVGA3D_B8G8R8X8_TYPELESS surface format.
With this patch, we will also check for SVGA3D_B8G8R8X8_UNORM surface format,
and use SVGA3D_B8G8R8X8_UNORM as the view format for that case.

Reviewed-by: Brian Paul <brianp@vmware.com>