drm/i915/lnl: Start using CDCLK through PLL

Introduce correspondent definitions for choosing between CD2X CDCLK
and PLL CDCLK as a source. All the entries in cdclk table for xe2lpd are
defined with PLL CDCLK as source, so simply set it. Also
skl_cdclk_decimal() shouldn't be set in CDCLK_CTL anymore, so skip it
for display version 20 and above.

v2:
  - Remove unneeded comment and use REG_BIT() (Matt Roper)
  - Rename CDCLK_SOURCE_SEL_CDCLK_PLL() to MDCLK_SOURCE_SEL_CDCLK_PLL
    to match spec (Lucas)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919192128.2045154-22-lucas.demarchi@intel.com