drm/i915/skl/kbl: Add support for pipe fusing

On SKL and KBL we can have pipe A/B/C disabled by fuse settings. The
pipes must be fused in descending order (e.g. C, B+C, A+B+C). We simply
decrease info->num_pipes if we find a valid fused out config.

v2: Don't store the pipe disabled mask in device info (Damien)

v3: Don't check FUSE_STRAP register for pipe c disabled

Cc: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
[Jani: fixed some checkpatch indentation complaints]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453300280-10661-1-git-send-email-patrik.jakobsson@linux.intel.com