ir3/compiler: Enable lower_io_offsets pass and handle new SSBO intrinsics

ir3/compiler: Enable lower_io_offsets pass and handle new SSBO intrinsics

These intrinsics have the offset in dwords already computed in the last
source, so the change here is basically using that instead of emitting
the ir3_SHR to divide the byte-offset by 4.

The improvement in shader stats is significant, of up to ~15% in
instruction count in some cases. Tested only on a5xx.

shader-db is unfortunately not very useful here because shaders that use
SSBO require GLSL versions that are not supported by freedreno yet.

For examples, most Khronos CTS tests under 'dEQP-GLES31.functional.ssbo.*'
are helped.

A random case:

dEQP-GLES31.functional.ssbo.layout.2_level_array.packed.row_major_mat3x2

with current master:

; CL prog 14/1: 1252 instructions, 0 half, 48 full
; 8 const, 8 constlen
; 61 (ss), 43 (sy)

with the SSBO dword-offset moved to NIR:

; CL prog 14/1: 1053 instructions, 0 half, 45 full
; 7 const, 7 constlen
; 34 (ss), 73 (sy)

The SHR previously emitted for every single SSBO instruction disappears
in most cases, and the dword-offset ends up embedded in the STGB
instruction as immediate in many cases as well.

There are also a few of those tests that are currently failing on register
allocation, that start to pass as a result of reducing the pressure. At least
these, probably more:

dEQP-GLES31.functional.ssbo.layout.random.unsized_arrays.24
dEQP-GLES31.functional.ssbo.layout.random.arrays_of_arrays.6
dEQP-GLES31.functional.ssbo.layout.random.arrays_of_arrays.17
dEQP-GLES31.functional.ssbo.layout.random.nested_structs_arrays.14
dEQP-GLES31.functional.ssbo.layout.random.nested_structs_arrays_instance_arrays.5
dEQP-GLES31.functional.ssbo.layout.random.nested_structs_arrays_instance_arrays.7

No regressions observed with relevant CTS and piglit tests.

Reviewed-by: Rob Clark <robdclark@gmail.com>