firmware: move printing of welcome banner to common function print_banner()

This unifies the printing of the welcome banner, and it also ensures
that all modes print all information (serial number, reset cause).

Furthermore the APP and BOARD #defines from the make environment are
also printed.

Change-Id: I7e6bc05cee4b9ec0fd9a05dc90ce0b26a5763e5a

firmware/libcommon/include/main_common.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void print_banner(void);