doc: doxygen: add support for function properties

Add aliases for setting function properties. A function may have 0, one
or more function properties. Example usage:

@funcprops \isr_ok, \async

These aliases will translate to API Terminology references when Doxygen
is rendered on Sphinx. On the Doxygen side they will just translate to
plain text.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>