manager: extend performance measurement interface to include firmware/loader times

manager: extend performance measurement interface to include firmware/loader times

This only adds the fields to the D-Bus interfaces but doesn't fill them
in with anything useful yet. Gummiboot exposes the necessary bits of
information to use however and as soon as I get my fingers on a proper
UEFI laptop I'll hook up the remaining bits.

Since we want to stabilize the D-Bus interface soon and include it in
the stability promise we should get the last fixes in, hence this change
now.