[PATCH] ppc64: set/clear SMT capable bit at boot

Allow the SMT bit to be set/reset at boot, like the ALTIVEC bit.  This
means we will enable SMT on unknown cpus that support it.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>