Bluetooth: EWS: rewrite handling Supervisory (S) bits

Supervisory bits occupy different windows in standard / extended control
fields. Convert hardcoded masks to relative ones and use shift to access
S-bit window.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>