drm/i915/psr: Read all Panel Replay capability registers from DPCD

There are several Panel Replay capability register in DPCD. Read them
all for later use.

v2:
  - avoid using hardcoded indices
  - read all Panel Replay capability registers

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://lore.kernel.org/r/20250526120512.1702815-4-jouni.hogander@intel.com