drm/xe: Move CCS enablement to engine setup RTP

Most register programming for engine setup happens via RTP tables in
hw_engine_setup_default_state().  Move the programming of RCU_MODE[0]
which enables the platform's CCS engine(s) there.  This both makes the
code more consistent (other RCU_MODE register programming is already
happening in this RTP table) and improves debuggability (since RTP
contents and checks of their correct programming are exposed via
debugfs).  It also helps consolidate the regular driver initialization
paths with the vestigial and currently unused execlist (i.e., non-GuC)
initialization.

With the original programming, the RCU_MODE register (which is a single
global register, not a per-engine register) was getting re-programmed
with the same value during the initialization of each CCS engine.  When
moved to the RTP table, we use the xe_rtp_match_first_render_or_compute
match function so that it will just be programmed once, while doing the
initialization for the first RCS/CCS engine, which avoids the redundant
and unnecessary repetition.

We can also safely drop the explicit addition of RCU_MODE from the GuC
ADS save-restore list now since all registers programmed via RTP tables
are automatically added to the GuC's list.

v2:
 - Only enable CCS engines on Xe_HP and later.  Even though Xe_LP
   platforms technically have a CCS engine, it's never been enabled on
   i915 or Xe due to other issues on these old platforms.

Reviewed-by: Shuicheng Lin <shuicheng.lin@intel.com>
Link: https://patch.msgid.link/20260424-engine-setup-v2-1-59cc620a25f1@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

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