drm/i915: Fix g4x cxsr enable condition

drm/i915: Fix g4x cxsr enable condition

The intention was to check whether the primary plane is enabled
without any sprites planes being enabled. Instead we ended up checking
whether just any one of the planes is enabled. g4x isn't vlv/chv and
cxsr only works with the primary plane. Fix the check to examine the
bitmask of active planes rather than the number of bits set in said
bitmask.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514125751.17075-3-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>