ARM: dts: msm: Add support to enable phy vls clamp for 9640

HPG recommends clamping phy level shifters by asserting
usb3_phy_vls_clamp_en. This is required for phy to perform
autonomous detection. Not setting the clamp properly may
leave phy in indeterminate state. In case of high speed bus
suspend followed by xo shutdown it is observed that qmp phy
is unnecessarily generating lfps rxterm interrupt and causing
mpm to wakeup APPS.

Change-Id: I95205988abc3f87073343f13e07e91158720d14b
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>