ac/llvm: load 1 byte at a time if unaligned on gfx10

ac/llvm: load 1 byte at a time if unaligned on gfx10

If buffer or stride is unaligned we use the same trick as on gfx6:
load 1 byte at a time and recompose the output if needed.
This change fixes lots of deqp/glcts tests:
  - dEQP-GLES2.functional.draw.random.1, 10, ...
  - dEQP-GLES2.functional.vertex_arrays.multiple_attributes.stride.3_float2_0_float2_0_float2_17, ...
  - dEQP-GLES2.functional.vertex_arrays.single_attribute.first.byte_first24_offset1_stride2_quads256, ...
  - dEQP-GLES2.functional.vertex_arrays.single_attribute.strides.buffer_0_17_byte2_vec4_dynamic_draw_quads_1, ...
  - dEQP-GLES31.functional.draw_indirect.random.14, ...

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5502>