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/drivers/clk/Makefile b/drivers/clk/Makefile
index 1a45bf3..37dfd28 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -38,5 +38,6 @@
 obj-$(CONFIG_MACH_PIC32) += clk_pic32.o
 obj-$(CONFIG_SANDBOX) += clk_sandbox.o
 obj-$(CONFIG_SANDBOX) += clk_sandbox_test.o
+obj-$(CONFIG_SANDBOX_CLK_CCF) += clk_sandbox_ccf.o
 obj-$(CONFIG_STM32H7) += clk_stm32h7.o
 obj-$(CONFIG_CLK_TI_SCI) += clk-ti-sci.o