drm/i915/dsi: separate clock and data lane prepare timing

drm/i915/dsi: separate clock and data lane prepare timing

The history of why the max of VBT clock and data lane prepare timing
parameter is used for both instead of each individually is
unknown. Separate them to follow what the Windows driver does.

Cc; William Tseng <william.tseng@intel.com>

Reviewed-by: William Tseng <william.tseng@intel.com>
Tested-by: William Tseng <william.tseng@intel.com>
Link: https://lore.kernel.org/r/079a26d0aae79f299aee0397dad2d6519cd55071.1743682608.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>