snapdragon: added msm_board_serial() func

This commit adds a function to get the board
serial number.
In snapdragon it's actually the eMMC serial number.

Function added in a new file misc.c that will
include further snapdragon miscellaneous functions.

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
diff --git a/arch/arm/mach-snapdragon/include/mach/misc.h b/arch/arm/mach-snapdragon/include/mach/misc.h
new file mode 100644
index 0000000..5af6ae8
--- /dev/null
+++ b/arch/arm/mach-snapdragon/include/mach/misc.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Snapdragon DRAM
+ * Copyright (C) 2018 Ramon Fried <ramon.fried@gmail.com>
+ */
+
+#ifndef MISC_H
+#define MISC_H
+
+u32 msm_board_serial(void);
+
+#endif