amd/registers: clean up gfx103.json

amd/registers: clean up gfx103.json

because gfx103.json is automatically generated and can't be changed
manually. This fixes the file generator without changing the generated
header.

Missing registers must be in registers-manually-defined.json, and
missing fields must be in parse_kernel_headers.py.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10261>