drm/i915: Check plane configuration properly

Checking with hweight8 if plane configuration had
changed seems to be wrong as different plane configs
can result in a same hamming weight.
So lets check the bitmask itself.

v2: Fixed "from" field which got corrupted for some weird reason

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200520145827.15887-1-stanislav.lisovskiy@intel.com