freedreno: Fix "Offset of packed bitfield changed" warnings:

freedreno: Fix "Offset of packed bitfield changed" warnings:

Example:

../src/freedreno/ir2/instr-a2xx.h:384:1: note: offset of packed bit-field
‘const_index’ has changed in GCC 4.4
  384 | } instr_fetch_vtx_t;

It's apparently due to bitfields that would cross the width of their type.
Just expand the types of the affected fields so that the compiler quiets
down.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6165>