drm/i915/cnl: DDI - PLL mapping

One of the steps for PLL (un)initialization is to (un)map
the correspondent DDI that is actually using that PLL.

So, let's do this step following the places already stablished
and used so far, although spec put this as part of PLL
initialization sequences.

v2: Use proper prefix on bits names as suggested by Ander.
v3: Add missed "~". Without that the logic was inverted
    so we were disabling interrupts.
    Credits-to: Clinton
    Credits-to: Art
v4: Spec is getting updated to do DDI -> PLL mapping
    and clock on in 2 separated reg writes. (Paulo)
    Also update bits definitions to use space
    (1 << 1) instead of (1<<1). (Paulo)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Art Runyan <arthur.j.runyan@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Kahola, Mika <mika.kahola@intel.com>
Cc: Ander Conselvan De Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Kahola, Mika <mika.kahola@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497047175-27250-5-git-send-email-rodrigo.vivi@intel.com