freedreno/afuc: Fix PM4 enum parsing

We were open-coding it, and getting variant parsing wrong for things
like "A4XX-" which don't explicitly include the version being
disassembled. Use the rnn function instead. This makes CP_INDIRECT show
up again. Also propagate const-ness to users.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6140>
1 file changed