[PATCH] x86_64: eliminate set_debug()

For consistency and to have only a single place of definition, replace
set_debug() uses with set_debugreg(), and eliminate the definition of
thj former.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>