usb: phy: qusb: Add tune2 module param to override TUNE2 value

QUSB PHY needs fine tuning of TUNE2 value. Hence add tune2 module
param to override default TUNE value when it is needed.

Change-Id: If986cae7d7812a87869fcb2b631fd37f7bbfb126
Signed-off-by: Mayank Rana <mrana@codeaurora.org>