clk: at91: add PLLADIV driver

As said in the SAMA5D2 datasheet, the PLLA clock must be divided
by 2 by writing the PLLADIV2 bit in PMC_MCKR, if the ratio between
PCK and MCK is 3 (MDIV = 3). This is the purpose of the driver.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
diff --git a/drivers/clk/at91/Makefile b/drivers/clk/at91/Makefile
index 8cac3f9..8c197ff 100644
--- a/drivers/clk/at91/Makefile
+++ b/drivers/clk/at91/Makefile
@@ -3,7 +3,7 @@
 #
 
 obj-y += pmc.o sckc.o
-obj-y += clk-slow.o clk-main.o clk-plla.o clk-master.o
+obj-y += clk-slow.o clk-main.o clk-plla.o clk-plladiv.o clk-master.o
 obj-y += clk-system.o clk-peripheral.o
 
 obj-$(CONFIG_AT91_UTMI)		+= clk-utmi.o