Various fixes to cbfstool.

Various fixes to cbfstool.

- add ntohll and htonll (as coreboot parses 64bit fields now)
- use the same byte swapping code across platforms
- detect endianess early
- fix lots of warnings
- Don't override CFLAGS in Makefile

Change-Id: Iaea02ff7a31ab6a95fd47858d0efd9af764a3e5f
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/313
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>