usb: qmp: phy: Remove PIPE3 clock switch related functionality

On 9x35 platform it was required to explicitly set PIPE3 clock to
19.2 MHz before performing QMP PHY initialization to generate 125 MHz
PIPE3 clock. Hence remove this functionality as it is not required on
newer platforms.

It is also recommended to turn ON pipe clock to controller when QMP
PHY is into power down state. Hence make necessary change for the same.

Change-Id: I37d8046618e007bb764899b3b73b10f132e0079c
Signed-off-by: Mayank Rana <mrana@codeaurora.org>