radeonsi: add AMD_DEBUG=elements for printing vertex elements

radeonsi: add AMD_DEBUG=elements for printing vertex elements

in si_create_vertex_elements()

This information is useful in debugging shader inputs/outputs

Sample output:
AMD_DEBUG=elements ./bin/arb_vertex_attrib_64bit-overlapping-locations shader -auto
elements[0]: offset  0, buffer_index 0, dual_slot 0, format  16, divisor 0
elements[1]: offset 16, buffer_index 0, dual_slot 0, format  16, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 104, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 105, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 106, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 107, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format  16, divisor 0
elements[1]: offset 16, buffer_index 0, dual_slot 0, format  16, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 104, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 105, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 106, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 107, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 107, divisor 0
elements[1]: offset 16, buffer_index 0, dual_slot 1, format 107, divisor 0
elements[2]: offset 32, buffer_index 0, dual_slot 1, format 105, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 107, divisor 0
elements[1]: offset 40, buffer_index 0, dual_slot 1, format 107, divisor 0
elements[2]: offset 56, buffer_index 0, dual_slot 1, format 105, divisor 0
elements[0]: offset  0, buffer_index 0, dual_slot 0, format 107, divisor 0
elements[1]: offset 64, buffer_index 0, dual_slot 1, format 107, divisor 0
elements[2]: offset 80, buffer_index 0, dual_slot 1, format 105, divisor 0

PIGLIT: {"result": "pass" }
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19570>