arm/dt: msm8974: Tune HS PHY init sequence for USB3

Currently HS DC volatge level adjustment(TXVREFTUNE) parameter is
set to value of 0xA in PARAMETER_OVERRIDE_B PHY register for USB3.
Based on experiments performed on this target, SW has to set this
TXVREFTUNE parameter to value of 0x8. Hence tune the HS PHY init
sequence accordingly for USB3.

Change-Id: I49b56a23c602b5f582c830a6c6ad7e75461191fc
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>