usb: otg: Add usb_hs_system_clk to OTG driver for MSM9615

This change add usb system clock support to OTG Driver.
System clock is a 60MHZ input clock to the USB ChipIdea core.
This clock is required starting from MDM9615.

This change also removes the enforcement for using a phy_reset_clk
for reseting the PHY. Starting from MDM9615, PHY reset is not implemented.
The core is reset together with the PHY using "usb_hs_clk" signal.

Change-Id: Ifa4155269dd46a97a7e57dd28050663a12f54c70
Signed-off-by: Amit Blay <ablay@codeaurora.org>