drm/i915/dg2: Support 4k@30 on HDMI

drm/i915/dg2: Support 4k@30 on HDMI

This patch adds a fix to support 297MHz of dot clock by calculating
the pll values using synopsis algorithm.
This will help to support 4k@30 mode for HDMI monitors on DG2.

v2: As per the algorithm, set MPLLB VCO range control bits to 3,
in register SNPS_PHY_MPLLB_DIV for 297Mhz. (Matt)

v3: Fix typo. (Ankit)

Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220525080401.1253511-1-ankit.k.nautiyal@intel.com