i965: expose type of memcpy instead of memcpy function itself

i965: expose type of memcpy instead of memcpy function itself

There is currently no use of returned memcpy functions outside
intel_tiled_memcpy. Patch changes intel_get_memcpy to return memcpy
type instead of actual function. This makes it easier later to separate
streaming load copy in to own static library.

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>