drm/i915/icl: add basic support for the ICL clocks

This commit introduces the definitions for the ICL clocks and adds the
basic functions to the shared DPLL framework. It adds code for the
Enable and Disable sequences for some PLLs, but it does not have the
code to compute the actual PLL values, which are marked as TODO
comments and should be introduced as separate commits.

Special thanks to James Ausmus for investigating and fixing a bug with
the placement of icl_unmap_plls_to_ports() function.

v2:
 - Rebase around dpll_lock changes.
v3:
 - The spec now says what the timeouts should be.
 - Touch DPCLKA_CFGCR0_ICL at the appropriate time so we don't freeze
   the machine.
 - Checkpatch found a white space problem.
 - Small adjustments before upstreaming.
v4:
 - Move the ICL checks out of the *map_plls_to_ports() functions
  (James)
 - Add extra encoder check (James)
 - Call icl_unmap_plls_to_ports() later (James)
v5:
 - Rebase after the pll struct changes.
v6:
 - Properly make the unmap function based on encoders_post_disable()
   with regarding to checks and iterators.
 - Address checkpatch comment on "min = max = x()".

Cc: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180427231436.9353-1-paulo.r.zanoni@intel.com