drm/i915/gt: Use parameterized RING_MI_MODE

We have both a parameterized RING_MI_MODE() macro and an RCS-specific
MI_MODE; drop the latter and use the former everywhere.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209051140.1599643-4-matthew.d.roper@intel.com