agx: Inline 16-bit load/store offsets

agx: Inline 16-bit load/store offsets

Most integer immediates are only 8-bit, but load/store instructions allow their
immediate offsets to be 16-bit instead. Take advantage of this in the optimizer.
This eliminates 36% of the instructions in
dEQP-GLES31.functional.ssbo.layout.random.all_shared_buffer.36, a fitting
percentage.

Insignificant effect on dEQP-GLES31.functional.ssbo.* performance... Only a
small % of our compile-time pie is actually spent in the backend anyway (as
opposed to NIR passes or GLSL IR).

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21430>