i965/vec4: Use MOV_INDIRECT instead of reladdr for indirect push constants

i965/vec4: Use MOV_INDIRECT instead of reladdr for indirect push constants

This commit moves us to an instruction based model rather than a
register-based model for indirects.  This is more accurate anyway as we
have to emit instructions to resolve the reladdr.  It's also a lot simpler
because it gets rid of the recursive reladdr problem by design.

One side-effect of this is that we need a whole new algorithm in
move_uniform_array_access_to_pull_constants.  This new algorithm is much
more straightforward than the old one and is fairly similar to what we're
already doing in the FS backend.