iommu/arm: fix ARM_SMMU_QCOM compilation

My previous bugfix ended up making things worse for the QCOM IOMMU
driver when it forgot to add the Kconfig symbol that is getting used to
control the compilation of the SMMU implementation specific code
for Qualcomm.

Fixes: 424953cf ("qcom_scm: hide Kconfig symbol")
Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reported-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reported-by: John Stultz <john.stultz@linaro.org>
Link: https://lore.kernel.org/lkml/20211010023350.978638-1-dmitry.baryshkov@linaro.org/Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/iommu/Kconfig

@@ -355,6 +355,14 @@ config ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT
 	  'arm-smmu.disable_bypass' will continue to override this
 	  config.
 
+config ARM_SMMU_QCOM
+	def_tristate y
+	depends on ARM_SMMU && ARCH_QCOM
+	select QCOM_SCM
+	help
+	  When running on a Qualcomm platform that has the custom variant
+	  of the ARM SMMU, this needs to be built into the SMMU driver.
+
 config ARM_SMMU_V3
 	tristate "ARM Ltd. System MMU Version 3 (SMMUv3) Support"
 	depends on ARM64