commonlib/bsd: Add new CBFS core implementation

This patch adds a new CBFS implementation that is intended to replace
the existing commonlib/cbfs.c. The new implementation is designed to
meet a bunch of current and future goals that in aggregate make it
easier to start from scratch than to adapt the exisiting implementation:

1. Be BSD-licensed so it can evetually be shared with libpayload.
2. Allow generating/verifying a master hash for future CBFS per-file
   verification (see [1][2]).
3. Be very careful about reading (not mmaping) all data only once, to be
   suitable for eventual TOCTOU-safe verification.
4. Make it possibly to efficiently implement all current and future
   firmware use cases (both with and without verification).

The main primitive is the cbfs_walk() function which will traverse a
CBFS and call a callback for every file. cbfs_lookup() uses this to
implement the most common use case of finding a file so that it can be
read. A host application using this code (e.g. coreboot, libpayload,
cbfstool) will need to provide a <cbfs_glue.h> header to provide the
glue to access the respective CBFS storage backend implementation.

This patch merely adds the code, the next patch will integrate it into
coreboot.

[1]: https://www.youtube.com/watch?v=Hs_EhewBgtM
[2]: https://osfc.io/uploads/talk/paper/47/The_future_of_firmware_verification_in_coreboot.pdf

Change-Id: Ica64c1751fa37686814c0247460c399261d5814c
Signed-off-by: Julius Werner <jwerner@chromium.org>
---
M MAINTAINERS
A src/commonlib/bsd/cbfs_private.c
M src/commonlib/bsd/include/commonlib/bsd/cb_err.h
A src/commonlib/bsd/include/commonlib/bsd/cbfs_private.h
M src/commonlib/bsd/include/commonlib/bsd/cbfs_serialized.h
5 files changed, 269 insertions(+), 5 deletions(-)