clk: scmi: Add Kconfig option for SPL

Building U-Boot SPL with CLK_SCMI and SCMI_FIRMWARE Kconfig options
enabled and SPL_FIRMWARE disabled result in the following error.

  drivers/clk/clk_scmi.o: in function `scmi_clk_gate':
  drivers/clk/clk_scmi.c:84: undefined reference to `devm_scmi_process_msg'
  drivers/clk/clk_scmi.c:88: undefined reference to `scmi_to_linux_errno'
  drivers/clk/clk_scmi.o: in function `scmi_clk_get_rate':
  drivers/clk/clk_scmi.c:113: undefined reference to `devm_scmi_process_msg'
  drivers/clk/clk_scmi.c:117: undefined reference to `scmi_to_linux_errno'
  drivers/clk/clk_scmi.o: in function `scmi_clk_set_rate':
  drivers/clk/clk_scmi.c:139: undefined reference to `devm_scmi_process_msg'
  drivers/clk/clk_scmi.c:143: undefined reference to `scmi_to_linux_errno'
  drivers/clk/clk_scmi.o: in function `scmi_clk_probe':
  drivers/clk/clk_scmi.c:157: undefined reference to `devm_scmi_of_get_channel'
  make[1]: *** [scripts/Makefile.spl:527: spl/u-boot-spl] Error 1
  make: *** [Makefile:2043: spl/u-boot-spl] Error 2

Add Kconfig option so that CLK_SCMI can be disabled in SPL to fix this.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 42280cb..19269c7 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -166,6 +166,14 @@
 	  by a SCMI agent based on SCMI clock protocol communication
 	  with a SCMI server.
 
+config SPL_CLK_SCMI
+	bool "Enable SCMI clock driver in SPL"
+	depends on SCMI_FIRMWARE && SPL_FIRMWARE
+	help
+	  Enable this option if you want to support clock devices exposed
+	  by a SCMI agent based on SCMI clock protocol communication
+	  with a SCMI server in SPL.
+
 config CLK_HSDK
 	bool "Enable cgu clock driver for HSDK boards"
 	depends on CLK && TARGET_HSDK