include/linux: Add bsg.h to the Kernel exported headers

bsg.h in current form is perfectly suitable for user-mode
consumption. It is needed together with scsi/sg.h for applications
that want to interface with the bsg driver.

Currently the few projects that use it would copy it over into
the projects. But that is not acceptable for projects that need
to provide source and devel packages for distros.

This should also be submitted to stable 2.6.28 and 2.6.27 since bsg had
a stable API since these Kernels and distro users will need the header
for these kernels a swell

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
CC: stable@kernel.org
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>