radv: add and use radv_vs_input_alpha_adjust

Unlike ac_fetch_format, this enum can be packed into two bits.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11717>
5 files changed