soc: qcom: smsm: Add missing mailbox dependency to Kconfig

Since the smsm driver got the ability to interact with the mailbox using
the mailbox subsystem and not just syscon, we need to add the dependency
to kconfig as well to avoid compile errors.

Fixes: 75287992 ("soc: qcom: smsm: Support using mailbox interface")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406180006.Z397C67h-lkp@intel.com/Signed-off-by: Luca Weiss <luca@lucaweiss.eu>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20240628-smsm-kconfig-v1-1-117d5af4ba1f@lucaweiss.euSigned-off-by: Bjorn Andersson <andersson@kernel.org>

drivers/soc/qcom/Kconfig

@@ -211,6 +211,7 @@ config QCOM_SMP2P
 
 config QCOM_SMSM
 	tristate "Qualcomm Shared Memory State Machine"
+	depends on MAILBOX
 	depends on QCOM_SMEM
 	select QCOM_SMEM_STATE
 	select IRQ_DOMAIN