This patch introduces the subnodes <provides>, <requires>, and
<content> to the <runtime> node. All <rom> sessions that are
expected from the depot appear within the <content> node, which
sets them nicely apart from <rom> sessions that may be required
as runtime arguments.
Note that the <requires> and <provides> nodes do not appear in the
patch because the existing depot_deploy tool does not interpret this
information (the pkg/test-fs_report runtime does not provide any
service, and the timer session is provided as a common route).
By specifying the 'config' of a '<runtime>' as an attribute, we can
distinguish the case where the config is obtained from a ROM session
from the case where the config is specified inline as a '<config>' node.
