i965/cnl: Make URB {VS, GS, HS, DS} sizes non multiple of 3

i965/cnl: Make URB {VS, GS, HS, DS} sizes non multiple of 3

v1: By Ben Widawsky <benjamin.widawsky@intel.com>
v2: v1 had an assert only for VS. Add the restriction for GS, HS and
    DS as well and make sure the allocated sizes are not multiple of 3.
v3: Move the entry_size checks in to compiler code (Ken)

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>