freedreno/ir3: ir3_cmdline updates

freedreno/ir3: ir3_cmdline updates

1) convert to getopt, and drop most variant related options since
   they aren't super-useful these days.. and easy enough to add
   back if/when needed.  (Also, none of the newer shader variant
   options where covered before.)
2) covert to dynamically allocated shader/variant, to get things
   working again after ir3_shader/_variant converted to ralloc
3) few small cleanups

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6189>