ARM: multi_v7_defconfig: Enable STM32 IPCC mailbox driver

The STM32 systems have a mailbox used for communication with non-Linux
processors like the M4 on the STM32MP157A.  Enable the driver for the
mailbox so it is available for testing.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240107-arm-defconfig-stm32-ipcc-v1-1-924721db5661@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/configs/multi_v7_defconfig

@@ -1075,6 +1075,7 @@ CONFIG_OMAP2PLUS_MBOX=y
 CONFIG_BCM2835_MBOX=y
 CONFIG_QCOM_APCS_IPC=y
 CONFIG_QCOM_IPCC=y
+CONFIG_STM32_IPCC=m
 CONFIG_OMAP_IOMMU=y
 CONFIG_OMAP_IOMMU_DEBUG=y
 CONFIG_ROCKCHIP_IOMMU=y