x86: Update docs link in bootparam header

After Linux commit ff61f0791ce9, x86 documentation was moved to
arch/x86 and the link in bootparam.h was broken.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
1 file changed