ARM: dts: msm: Add nvmem property in qusb_phy on SDM670

This property will be used to distinguish between different
SoC versions to simplify applying chip version specific
work-arounds.

Change-Id: I7ce6cac074c0fa851078f1925e8dcd5a93fac37b
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>