radv,aco: track if a fragment shader needs an epilog

radv,aco: track if a fragment shader needs an epilog

This is currently disabled but it will be used for testing first,
and then for graphics pipeline libraries.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17485>