drm/i915/glk: Program txesc clock divider for GLK

v2: Addressed Jani's Review comments(renamed bit field macros)

Txesc clock divider is calculated and programmed
for geminilake platform.

Signed-off-by: Deepak M <m.deepak@intel.com>
Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487335415-14766-7-git-send-email-madhav.chauhan@intel.com