bcm2835_mu_serial: Convert to Kconfig

Setting config options using headers is deprecated. This patch converts
the BCM2835 Mini-UART to Kconfig.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 4167683..72281a7 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -388,6 +388,13 @@
 	  configured in the device tree, and input clock frequency can
 	  be got from the clk node.
 
+config BCM283X_MU_SERIAL
+	bool "Support for BCM283x Mini-UART"
+	depends on DM_SERIAL && ARCH_BCM283X
+	default y
+	help
+	  Select this to enable Mini-UART support on BCM283X family of SoCs.
+
 config BCM6345_SERIAL
 	bool "Support for BCM6345 UART"
 	depends on DM_SERIAL && ARCH_BMIPS