drm/i915/icl: Fix PLL mapping sanitization for DP ports

We shouldn't consider an encoder inactive if it doesn't have a CRTC
linked, but has virtual MST encoders with a crtc linked. Fix this.

Also we should not sanitize the mapping for MST encoders, as it's always
their primary encoder (which could be even in SST mode) whose active
state determines if we need the clock being enabled for the
corresponding physical port. Fix this too.

This fixes at least an existing breakage where we incorrectly disabled
the clock for an active DP encoder when sanitizing its MST virtual
encoders. Not sure if there are BIOSes that enable an output in MST
mode, but our HW readout is mostly missing for it anyway, so just warn
for that case.

Fixes: 70332ac5 ("drm/i915/icl+: Sanitize port to PLL mapping")
Cc: Antonio Argenziano <antonio.argenziano@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reported-by: Antonio Argenziano <antonio.argenziano@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Tested-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181107200836.10191-2-imre.deak@intel.com