x86: fix up bootparam.h for userspace inclusion

commit 8b664aa6 (x86, boot: add linked
list of struct setup_data) put a new struct in bootparam.h, but didn't
use the userspace-safe types.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Huang Ying <ying.huang@intel.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Signed-off-by: Ingo Molnar <mingo@elte.hu>