haven: rm: Update dt parsing to match Haven-supplied nodes

Haven hypervisor provides RM dt entries in a slightly different format
than has been used. Namely: the compatible string, capids are now
described by "reg" property, VMID/owner vmid is in a sibling DT node,
and names of some properties are changed. Thus, update RM driver to
parse accordingly. Common message queue dt parsing was moved into the
msgq driver helper function "hh_msgq_probe".

Change-Id: If3fe026bb6055267705a19d8ed7fd90ef0934270
Signed-off-by: Elliot Berman <eberman@codeaurora.org>