x86: set SPECTRE_BHI_ON as default

commit 2bb69f5f upstream.

Part of a merge commit from Linus that adjusted the default setting of
SPECTRE_BHI_ON.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>