mailbox: mpfs: convert SOC_MICROCHIP_POLARFIRE to ARCH_MICROCHIP_POLARFIRE

As part of converting RISC-V SOC_FOO symbols to ARCH_FOO to match the
use of such symbols on other architectures, convert the Microchip FPGA
mailbox driver to use the new symbol.
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/Kconfig

@@ -176,7 +176,7 @@ config MAILBOX_TEST
 config POLARFIRE_SOC_MAILBOX
 	tristate "PolarFire SoC (MPFS) Mailbox"
 	depends on HAS_IOMEM
-	depends on SOC_MICROCHIP_POLARFIRE || COMPILE_TEST
+	depends on ARCH_MICROCHIP_POLARFIRE || COMPILE_TEST
 	help
 	  This driver adds support for the PolarFire SoC (MPFS) mailbox controller.