drm/i915/dsi: let HW maintain CLK_POST

drm/i915/dsi: let HW maintain CLK_POST

This change is to adjust TCLK-POST timing so DSI signaling can
meet CTS specification.

For clock lane, the TCLK-POST timing may be changed from
133.44 ns to 178.72 ns, which is greater than (60 ns+52*UI)
and is conformed to the CTS standard.

The computed UI is around 1.47 ns.

v2: remove the change of HS-TRAIL.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: William Tseng <william.tseng@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230914095137.4132029-1-william.tseng@intel.com