usb: phy: qmp: Add support to select usb3 phy mode

qmp phy can run in display port mode or in usb3 mode.
It is recommended to explicitly select the usb3 phy
mode before programming the phy init sequence, since
TCSR_USB3_DP_PHYMODE register is commonly used to
select mode between display port driver as well as
ssphy driver.

Change-Id: I270596868762ccd4f2f2cc9b0daaca647a2bee88
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>