vmware-vga: add vmsvga_verify_rect

Add verification function for rectangles, returning
true if verification passes and false otherwise.

Cc: qemu-stable@nongnu.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Don Koch <dkoch@verizon.com>
(cherry picked from commit 07258900)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>