ARM: dts: msm: Add rpm peripheral DT entry for MSM 8939

HLOS is responsible for configuring CB registers
when secure environment is disabled. Add rpm
peripheral CB entry in DT so as to enable HLOS to
configure rpm_periph context bank registers
during non secure environment.

Change-Id: I75fe52bc9db75b0f5728b335f69326b4b6a593f7
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>