By popular demand, define usefull wrappers for osd_req_read/write
that recieve kernel pointers. All users had their own.

Also remove these from exofs
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

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: NBoaz Harrosh <bharrosh@panasas.com>