ARM: dts: msm: Specify throughput threshold for IPA on SDX20

Different target supports different throughput threshold
bandwidth for NOM and TURBO clocks.

To support this add a new device tree node to set
tput threshold bandwidth.

With this change we can support to update a new threshold BW for
NOM and TURBO clocks during driver init.

Change-Id: I8f2850ee4db482997da856d3eefae9d89bf7a6a2
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>