drm/i915/cnl: Enable DDI-F on Cannonlake.

Now let's finish the Port-F support by adding the
proper port F detection, irq and power well support.

v2: Rebase
v3: Use BIT_ULL
v4: Cover missed case on ddi init.
v5: Update commit message.
v6: Rebase on top of display headers rework.
v7: Squash power-well handling related to DDI F to this
    patch to avoid warns as pointed out by DK.
v8: Introduce DDI_F_LANES to PG2. (DK)
v9: Squash in the PORT_F case for enabling DP MST encoder. (DK)

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180129232223.766-9-rodrigo.vivi@intel.com