drm/i915: add VLV DSI PLL Calculations

v2:
 - Grab dpio_lock mutex in vlv_enable_dsi_pll().
 - Add and call vlv_disable_dsi_pll().

v3: Mostly based on Ville's review comments.
 - Only pipe A has DSI PLL lock bit.
 - Add more of CCK REG bit definitions for DSI PLL.
 - Make tables static.
 - Move clock gating out of the clock calculation functions.
 - DSI PLL LDO power gating.
 - Put alternative MNP from table calc behind #ifdef.

v4: s/CKK/CLK/ in the CCK REG bit definitions (Ville).

Signed-off-by: ymohanma <yogesh.mohan.marimuthu@intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>