include: Bluetooth: Add LE Supported Features type to GAP

BT 5.3 Core Spec provides possibility to transmit LE Supported
Features in advertising data. The value is prepared as in
case of other advertising data by an application.
There was missing LE Supported Features advertising data type in
macros defined in gap.h.

Besides that, the commit provides set of macros that help
to encode 64-bit LE Supported Features data into advertising
data.
There is a set of macros because all 0x0 bytes after last
non-zero byte should be ommited.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>