broadcom/compiler: allow GLSL_SAMPLER_DIM_BUF on txs emission

broadcom/compiler: allow GLSL_SAMPLER_DIM_BUF on txs emission

Although we don't support texture buffers on the OpenGL driver, we are
already doing that for the Vulkan driver. This would be needed for the
OpenGL driver in any case.

Fixes following tests on v3dv:
 dEQP-VK.memory.pipeline_barrier.host_write_uniform_texel_buffer.*
 dEQP-VK.memory.pipeline_barrier.transfer_dst_uniform_texel_buffer.*

Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>