I8K: add i8k driver to the x86_64 Kconfig

Adds i8k driver to the x86_64 Kconfig.

Signed-off-by: Bradley Smith <bradjsmith@btinternet.com>
Cc: Frank Sorenson <frank@tuxrocks.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>