drm/i915: Make intel_bw_modeset_checks() internal to intel_bw_atomic_check()

drm/i915: Make intel_bw_modeset_checks() internal to intel_bw_atomic_check()

Now that all the sagv computation has been moved from the
skl+ watermark code into intel_bw_atomic_check() there is
no point in calling intel_bw_modeset_checks() before the
wm computation. Hide it within intel_bw_atomic_check().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250326162544.3642-13-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>