clk: sandbox: Add sandbox test code for Common Clock Framework [CCF]

This patch provides code to implement the CCF clock tree in sandbox. It
uses all the introduced primitives; some generic ones are reused, some
sandbox specific were developed.

In that way (after introducing the real CCF tree in sandbox) the recently
added to clk-uclass.c: clk_get_by_id() and clk_get_parent_rate() are tested
in their natural work environment.

Usage (sandbox_defconfig and sandbox_flattree_defconfig):
./u-boot --fdt arch/sandbox/dts/test.dtb --command "ut dm clk_ccf"

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 6a36cc0..9c5e860 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -17,7 +17,7 @@
 obj-$(CONFIG_BLK) += blk.o
 obj-$(CONFIG_BOARD) += board.o
 obj-$(CONFIG_DM_BOOTCOUNT) += bootcount.o
-obj-$(CONFIG_CLK) += clk.o
+obj-$(CONFIG_CLK) += clk.o clk_ccf.o
 obj-$(CONFIG_DM_ETH) += eth.o
 obj-$(CONFIG_FIRMWARE) += firmware.o
 obj-$(CONFIG_DM_GPIO) += gpio.o