drm/i915/cnl: Enable wrpll computation for CNL

Enable wrpll computation for Cannonlake platform to support
pll's required for HDMI output. The patch contains the following features

- compute Cannonlake port clock programming
  dividers P, Q, and K.
- compute PLL parameters for Cannonlake. These parameters
  set the values on DPLL registers.
- find the register values to program wrpll for Cannonlake.
  The reference clock can be either 19.2MHz or 24MHz.

v2: rebase
v3: squash wrpll patches into one (Rodrigo)
v4: switch order of getting even dividers (Paulo)
    update divider register values for PDiv and KDiv (Paulo)
    update wrpll computation algorithm (Paulo)
v5: Remove ref clock division by 1000. (Rodrigo)
v6: Rodrigo rebasing on top of latest code.

Signed-off-by: Kahola, Mika <mika.kahola@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497047175-27250-18-git-send-email-rodrigo.vivi@intel.com