Convert CONFIG_CMD_CLK to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_CLK

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: imply CMD_CLK on ARCH_ZYNQ]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0b70c47..513a35f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -676,6 +676,7 @@
 	select CLK
 	select SPL_CLK
 	select CLK_ZYNQ
+	imply CMD_CLK
 
 config ARCH_ZYNQMP
 	bool "Support Xilinx ZynqMP Platform"