i965/fs: Add support for MOV_INDIRECT on pre-Broadwell hardware

i965/fs: Add support for MOV_INDIRECT on pre-Broadwell hardware

While we're at it, we also add support for the possibility that the
indirect is, in fact, a constant.  This shouldn't happen in the common case
(if it does, that means NIR failed to constant-fold something), but it's
possible so we should handle it.

Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>