commonlib: add input and output buffer helpers

Introduce ibuf and obuf structures for helping manage memory buffers.
The ibuf, an input buffer, can be read from and the obuf, an output
buffer, can be written to. Helper functions are provided for serializing
values in different endian formats. This library is provided to for
common buffer management routines such that the same code doesn't
have to re-written in different and less consistent forms.

BUG=b:36598499

Change-Id: I5247237f68b658906ec6916bbbb286d57d6df5ee
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/19062
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>

src/commonlib/Makefile.inc

@@ -4,6 +4,13 @@ romstage-y += mem_pool.c
 ramstage-y += mem_pool.c
 postcar-y += mem_pool.c
 
+bootblock-y += iobuf.c
+verstage-y += iobuf.c
+romstage-y += iobuf.c
+ramstage-y += iobuf.c
+smm-y += iobuf.c
+postcar-y += iobuf.c
+
 bootblock-y += region.c
 verstage-y += region.c
 romstage-y += region.c