ARM: dts: msm: Add support mdm9x45 external modem

This change defines upto 3 instances of external mdm9x45 modems in
device-tree which would need to be controlled by esoc (external esoc)
driver. The device-tree nodes allows the configuration of the external
modems (like the GPIO pins used to communicate status of modem) to be
specified.

Change-Id: I7e609f7549a02cd3322db76b00dc30137ed68953
Signed-off-by: Arun KS <arunks@codeaurora.org>