advertising: Add SupportedFeatures to LEAdvertisingManager1

advertising: Add SupportedFeatures to LEAdvertisingManager1

The new SupportedFeatures member tells advertising clients whether the
platform has hardware support for advertising or capability to set tx
power of advertisements.

Additionally, fix small typo in "secondary_exists" function name.

Change is tested on hatch and kukui chromebooks by using dbus-send to
verify that SupportedFeatures always exists, and is only populated when
extended advertising is available.

Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>