hw/hppa/Kconfig: Fix building with "configure --without-default-devices"

hw/hppa/Kconfig: Fix building with "configure --without-default-devices"

When running "configure" with "--without-default-devices", building
of qemu-system-hppa currently fails with:

 /usr/bin/ld: libqemu-hppa-softmmu.fa.p/hw_hppa_machine.c.o: in function `machine_HP_common_init_tail':
 hw/hppa/machine.c:399: undefined reference to `usb_bus_find'
 /usr/bin/ld: hw/hppa/machine.c:399: undefined reference to `usb_create_simple'
 /usr/bin/ld: hw/hppa/machine.c:400: undefined reference to `usb_bus_find'
 /usr/bin/ld: hw/hppa/machine.c:400: undefined reference to `usb_create_simple'
 collect2: error: ld returned 1 exit status
 ninja: build stopped: subcommand failed.
 make: *** [Makefile:162: run-ninja] Error 1

And after fixing this, the qemu-system-hppa binary refuses to run
due to the missing 'pci-ohci' and 'pci-serial' devices. Let's add
the right config switches to fix these problems.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>