drm/i915/cnl: Initialize PLLs

Although CNL follows PLL initialization more like Skylake
than Broxton we have a completely different initialization
sequence and registers used.

One big difference from SKL is that CDCLK PLL is now
exclusive (ADPLL) and for DDIs and MIPI we need to use
DFGPLLs 0, 1 or 2.

v2: Accept all Ander's suggestions and fixes:
    - Registers and bits names prefix
    - Group pll functions
    - bits masks fixes
    - remove read and modify on cfgcr1
    - fix cfgcr0 setup
v3: Set SSC_ENABLE for DP.
    Fix HDMI_MODE cfgcr0.
    Avoid touch cfgcr0 on DP.
    Add missed else on dpll_mgr definition so we use cnl one, not hsw.
v3: Centra freq should be always set to default and change bits
    definitions to (1 << 1) instead of (1<<1). (by Paulo)
v4: Rebased.

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Kahola, Mika <mika.kahola@intel.com>
Reviewed-by: Ander Conselvan De Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497047175-27250-7-git-send-email-rodrigo.vivi@intel.com