msm: msm_bus: Add driver to fetch rpmh rsc clients

Change rpmh and command db APIS to match new version,
and add additional helper function to fetch device handles from
rsc nodes under rpmh.

Change-Id: Id2ae276105ba21eb313ee8acb83ca266db6064bc
Signed-off-by: David Dai <daidavid1@codeaurora.org>