firmware: imx: select SOC_BUS to fix firmware build

Fix build error in firmware/imx/ selecting SOC_BUS.

riscv32-linux-ld: drivers/firmware/imx/imx-scu-soc.o: in function `.L9':
imx-scu-soc.c:(.text+0x1b0): undefined reference to `soc_device_register'

Fixes: edbee095 ("firmware: imx: add SCU firmware driver support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Atish Patra <atish.patra@wdc.com>
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Anson Huang <Anson.Huang@nxp.com>
Cc: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/firmware/imx/Kconfig

@@ -13,6 +13,7 @@ config IMX_DSP
 config IMX_SCU
 	bool "IMX SCU Protocol driver"
 	depends on IMX_MBOX
+	select SOC_BUS
 	help
 	  The System Controller Firmware (SCFW) is a low-level system function
 	  which runs on a dedicated Cortex-M core to provide power, clock, and