drm/i915: Enable SDP split for DP2.0

Enable the SDP split configuration for DP2.0.

v2: Move the register handling out of compute config function (JaniN)

v3: Patch styling and register access based on platform support (JaniN)

v4: Rebased

v5: Use unconditional clear bit in intel_de_rmw (Jani Nikula)

Bspec: 67768
Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221121150718.1117628-1-vinod.govindapillai@intel.com