svga: eliminiate unnecessary constant buffer updates

svga: eliminiate unnecessary constant buffer updates

Currently if the texture binding is changed, emit_fs_consts()
is triggered to update texture scaling factor for
rectangle texture or texture buffer size in the constant buffer.
But the update is only relevant if the texture binding includes
a rectangle texture or a texture buffer.

To eliminate the unnecessary constant buffer updates due to other texture
binding changes, a new flag SVGA_NEW_TEXTURE_CONSTS will be used
to trigger fragment shader constant buffer update when a rectangle texture
or a texture buffer is bound.

With this patch, the number of constant buffer updates in Lightsmark2008
reduces from hundreds per frame to about 28 per frame.

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