alpha: select ARCH_MIGHT_HAVE_PC_PARPORT

Architectures which support CONFIG_PARPORT_PC should select
ARCH_MIGHT_HAVE_PC_PARPORT.

Signed-off-by: Mark Salter <msalter@redhat.com>
Acked-by: Richard Henderson <rth@twiddle.net>
CC: linux-alpha@vger.kernel.org