exofs: Kbuild, Headers and osd utils

This patch includes osd infrastructure that will be used later by
the file system.

Also the declarations of constants, on disk structures,
and prototypes.

And the Kbuild+Kconfig files needed to build the exofs module.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

diff --cc fs/exofs/Kbuild
Simple merge

diff --cc fs/exofs/Kconfig
Simple merge

diff --cc fs/exofs/common.h
Simple merge

diff --cc fs/exofs/exofs.h
Simple merge

diff --cc fs/exofs/osd.c
Simple merge