drm/i915/bxt: Additional MIPI clock divider form B0 stepping onwards

The MIPI clock calculations for the addtional clock
are revised from B0 stepping onwards, the bit definitions
have changed compared to old stepping.

v2: Fixing compilation warning.
v3: Retained the old Macros (Jani)

Signed-off-by: Deepak M <m.deepak@intel.com>
Tested-by: Ramalingam C <ramalingam.c@intel.com> # BXT-T with Tianma panel
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455556437-29267-1-git-send-email-m.deepak@intel.com