clk: at91: add USB Host clock driver

Add USB clock driver to configure the input clock and the divider
in the PMC_USB register to generate a 48MHz and a 12MHz signal to
the USB Host OHCI.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
diff --git a/drivers/clk/at91/Makefile b/drivers/clk/at91/Makefile
index fbe3cb6..8cac3f9 100644
--- a/drivers/clk/at91/Makefile
+++ b/drivers/clk/at91/Makefile
@@ -7,5 +7,6 @@
 obj-y += clk-system.o clk-peripheral.o
 
 obj-$(CONFIG_AT91_UTMI)		+= clk-utmi.o
+obj-$(CONFIG_AT91_USB_CLK)	+= clk-usb.o
 obj-$(CONFIG_AT91_H32MX)	+= clk-h32mx.o
 obj-$(CONFIG_AT91_GENERIC_CLK)	+= clk-generated.o