rmodule: add 16 bytes of padding

There is a plan to utlize rmodules for loading ramstage as a
relocatable module. However, the rmodule header may change.
In order to provide some wiggle room for changing the contents
of the rmodule header add some padding. This won't stop the need
for coordinating properly between the romstage loader that may be
in readonly flash and rmodule header fields.  But it will provide
for a way to make certain assumptions about alignment of the
rmodule's program when the rmodule is compressed in the flash.

Change-Id: I9ac5cf495c0bce494e7eaa3bd2f2bd39889b4c52
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2749
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/include/rmodule.h

@@ -100,6 +100,8 @@ struct rmodule_header {
 	/* BSS section information so the loader can clear the bss. */
 	u32 bss_begin;
 	u32 bss_end;
+	/* Add some room for growth. */
+	u32 padding[4];
 } __attribute__ ((packed));
 
 struct rmodule {