soc: kunpeng_hccs: add MAILBOX dependency

When the mailbox subsystem is disabled, the driver fails to link, so add
an explicit dependency. Some other drivers use 'select' here, but the
dependency seems more logical and more common.

Fixes: 886bdf9c ("soc: hisilicon: Support HCCS driver on Kunpeng SoC")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/soc/hisilicon/Kconfig

@@ -6,6 +6,7 @@ menu "Hisilicon SoC drivers"
 config KUNPENG_HCCS
 	tristate "HCCS driver on Kunpeng SoC"
 	depends on ACPI
+	depends on MAILBOX
 	depends on ARM64 || COMPILE_TEST
 	help
 	  The Huawei Cache Coherence System (HCCS) is a multi-chip