remoteproc: stm32: fix building without ARM SMCC

When compile testing this driver without SMCC support enabled,
we get a link error:

drivers/remoteproc/stm32_rproc.o: In function `stm32_rproc_start':
stm32_rproc.c:(.text+0x776): undefined reference to `__arm_smccc_smc'
drivers/remoteproc/stm32_rproc.o: In function `stm32_rproc_stop':
stm32_rproc.c:(.text+0x92c): undefined reference to `__arm_smccc_smc'

Make the actual call to arm_smccc_smc conditional on the Kconfig
symbol controlling its implementation.

Fixes: 13140de0 ("remoteproc: stm32: add an ST stm32_rproc driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/stm32_rproc.c

@@ -344,7 +344,7 @@ static int stm32_rproc_set_hold_boot(struct rproc *rproc, bool hold)
 
 	val = hold ? HOLD_BOOT : RELEASE_BOOT;
 
-	if (ddata->secured_soc) {
+	if (IS_ENABLED(CONFIG_HAVE_ARM_SMCCC) && ddata->secured_soc) {
 		arm_smccc_smc(STM32_SMC_RCC, STM32_SMC_REG_WRITE,
 			      hold_boot.reg, val, 0, 0, 0, 0, &smc_res);
 		err = smc_res.a0;