Patch from Bjorn Helgaas

I propose the following HCDP Kconfig patch.  It makes HCDP
selectable only when serial console has been selected.  One
desirable side effect is that both are then available only
when statically compiled in (i.e., not built as a module).

The HCDP support doesn't actually depend on IA64, but I left
that in for now because nobody else implements support for it
and I don't want people confused by a selectable option that
doesn't do anything.  Maybe a "depends on EFI" or something
will be useful eventually.