Make struct boot_params a real structure, and remove obsolete fields

Make struct boot_params a real structure, and remove the handling of
some obsolete fields, in particular hd*_info, which was only used by
the ST-506 driver, and likely to be wrong for that driver on any
modern BIOS.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>