serial: bcm6858: add serial support

This driver add the support of serial on bcm6858.
It's based on serial for bcm6345.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 597db4b..6625a65 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -500,6 +500,12 @@
 	help
 	  Select this to enable UART on BCM6345 SoCs.
 
+config BCM6858_SERIAL
+	bool "Support for BCM6858 UART"
+	depends on DM_SERIAL && ARCH_BCM6858
+	help
+	  Select this to enable UART on BCM6358 SoCs.
+
 config FSL_LINFLEXUART
 	bool "Freescale Linflex UART support"
 	depends on DM_SERIAL