drm/i915: Extract intel_bw_check_sagv_mask()

Move the bw_state->pipe_sagv_reject computation into intel_bw.c
where it belongs.

Previously we had a complicated dance between watermarks and
sagv which required this to be computed earlier, but that was
changed in commit 5e8146251f7b ("extract intel_bw_check_sagv_mask()")
which allows the whole thing to be cleaned up quite a bit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250326162544.3642-11-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>