drm/panelreplay: Panel Replay capability DPCD register definitions

Add new definition for size of Panel Replay DPCD capability registers
area. Rename existing definitions to group capability registers together.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://lore.kernel.org/r/20250526120512.1702815-2-jouni.hogander@intel.com