spl: Allow mailbox drivers to be used within SPL

Add an option for building mailbox drivers within SPL.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index e5a5188..cccd551 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -430,6 +430,14 @@
 	  boards. Enable this option to build the code in lib/ as part of an
 	  SPL build.
 
+config SPL_DM_MAILBOX
+	bool "Support Mailbox"
+	help
+	  Enable support for Mailbox within SPL. This enable the inter
+	  processor communication protocols tobe used within SPL. Enable
+	  this option to build the drivers in drivers/mailbox as part of
+	  SPL build.
+
 config SPL_MMC_SUPPORT
 	bool "Support MMC"
 	depends on MMC