ARM: dts: msm: remove pm-boot device node

Current pm-boot code handles TZ and non-TZ suported
processors. On recent targets TZ is enabled by default
and it is going to handle cores warmboot. This patch
removes the pm-boot device node and initialise the
driver as part of the system init calls.

Change-Id: Ie609d1e96e32f604f1bcc243197f04c356563e87
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>