config: allow DEBUG_IO for !QEMU

Make DEBUG_IO depend on QEMU_HARDWARE instead of QEMU, so
it can be enabled for seabios builds running indirectly
(coreboot, csm) on qemu.

Add runtime check for PF_QEMU to debug port console to make
sure we don't poke on random ports on physical hardware.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
coreboot: add qemu detection