drm/i915/adl_p: Add dedicated SAGV watermarks

XE_LPD reduces the number of regular watermark latency levels from 8
to 6 on non-dgfx platforms.  However the hardware also adds a special
purpose SAGV wateramrk (and an accompanying transition watermark) that
will be used by the hardware in place of the level 0 values during SAGV
transitions.

Bspec: 49325, 49326, 50419
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Clinton Taylor <Clinton.A.Taylor@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210519000625.3184321-4-lucas.demarchi@intel.com