st/xvmc: Include u_surface.h for u_copy_rect.

st/xvmc: Include u_surface.h for u_copy_rect.

This patch fixes the build error introduced with commit
81bb98e928861260170c16f5c3e0d80492251d6b.

  CC     subpicture.lo
subpicture.c: In function 'upload_sampler':
subpicture.c:181:4: error: implicit declaration of function 'util_copy_rect' [-Werror=implicit-function-declaration]
subpicture.c: In function 'XvMCClearSubpicture':
subpicture.c:304:21: error: storage size of 'uc' isn't known
subpicture.c:328:4: error: implicit declaration of function 'util_fill_rect' [-Werror=implicit-function-declaration]
subpicture.c:304:21: warning: unused variable 'uc' [-Wunused-variable]

Signed-off-by: Vinson Lee <vlee@freedesktop.org>