hw/intc/i8259: Fix Kconfig dependency on ISA bus

The 8259 Interrupt Controller sits on a ISA bus.
Add the missing dependency to fix:

    LINK    x86_64-softmmu/qemu-system-x86_64
  /usr/bin/ld: ../hw/intc/i8259_common.o: in function `pic_common_realize':
  hw/intc/i8259_common.c:84: undefined reference to `isa_register_ioport'
  /usr/bin/ld: hw/intc/i8259_common.c:86: undefined reference to `isa_register_ioport'
  /usr/bin/ld: ../hw/intc/i8259_common.o: in function `i8259_init_chip':
  hw/intc/i8259_common.c:97: undefined reference to `isa_create'
  collect2: error: ld returned 1 exit status
  make[1]: *** [Makefile:206: qemu-system-x86_64] Error 1

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191231183216.6781-3-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/intc/Kconfig

@@ -3,6 +3,7 @@ config HEATHROW_PIC
 
 config I8259
     bool
+    select ISA_BUS
 
 config PL190
     bool