arm: imx8mq: Add USB clock init function

Add clock function to setup relevant clocks for USB3.0 controllers and
PHYs on i.MX8MQ

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Patrick Wildt <patrick@blueri.se>
Tested-by: Patrick Wildt <patrick@blueri.se>

arch/arm/include/asm/arch-imx8m/clock.h

@@ -257,6 +257,7 @@ u32 imx_get_uartclk(void);
 int clock_init(void);
 void init_clk_usdhc(u32 index);
 void init_uart_clk(u32 index);
+void init_usb_clk(void);
 void init_wdog_clk(void);
 unsigned int mxc_get_clock(enum mxc_clock clk);
 int clock_enable(enum clk_ccgr_index index, bool enable);