phy: usb: qmp: Add com_aux_clk related support

On some platform, "com_aux_clk" is needed with USB QMP DP Combo PHY.
Hence add com_aux_clk related support and handling with this driver.
com_aux_clk is optional clock here.

Also this change creates separate API to handle required clocks instead
of using clk APIs from multiple places.

USB pipe clock is generated by QMP USB PHY itself. Hence it is not
needed to set clock rate explicitly using clk_set_rate() API. Usage of
clk_set_rate() is no-op here.

Change-Id: Ic8c065c648561bfeb9dc19dfbb549472451e0fc1
Signed-off-by: Mayank Rana <mrana@codeaurora.org>