TPM: NSC and TIS drivers X86 dependency fix

A previous commit removed its PNP dependency, that in fact wasn't
necessary, but also allowed it be built for other architectures not
supported by it. This then caused kernel oops on PPC based machines.
I'm placing a x86 dependency back correctly.

Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>