drm/i915/icl: Program TA_TIMING_PARAM registers

This patch programs D-PHY timing parameters for the
bus turn around flow(in escape clocks) only if dsi link
frequency <=800 MHz using DPHY_TA_TIMING_PARAM and its
identical register DSI_TA_TIMING_PARAM (inside DSI
Controller within the Display Core).

v2: Changes
    - Don't use KHz() macro (Ville/Jani N)
    - Use newly defined bitfields

v3 by Jani:
 - Use intel_dsi_bitrate() in favor of a new field
 - Remove redundant parens

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2c777092a748dfc973714399d8c19ed7a8c31a10.1539613303.git.jani.nikula@intel.com