drm/atomic: Add the crtc to affected crtc only if uapi.enable = true

In case of a modeset where a mode gets split across multiple CRTCs
in the driver specific implementation (bigjoiner in i915) we wrongly count
the affected CRTCs based on the drm_crtc_mask and indicate the stolen CRTC as
an affected CRTC in atomic_check_only().
This triggers a warning since affected CRTCs doent match requested CRTC.

To fix this in such bigjoiner configurations, we should only
increment affected crtcs if that CRTC is enabled in UAPI not
if it is just used internally in the driver to split the mode.

v3: Add the same uapi crtc_state->enable check in requested
crtc calc (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Simon Ser <contact@emersion.fr>
Cc: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.11+
Fixes: 919c2299

 ("drm/i915: Enable bigjoiner")
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211004115913.23889-1-manasi.d.navare@intel.com