hw/i386/Kconfig: Add missing Kconfig dependency (runtime error)

When building the 'microvm' machine stand-alone we get:

  $ qemu-system-x86_64 -M microvm
  **
  ERROR:qom/object.c:714:object_new_with_type: assertion failed: (type != NULL)
  Bail out! ERROR:qom/object.c:714:object_new_with_type: assertion failed: (type != NULL)
  Aborted (core dumped)

Looking at the backtrace:

  (gdb) bt
  #3  0x00007ff2330492ff in g_assertion_message_expr () at /lib64/libglib-2.0.so.0
  #4  0x000055a878c18341 in object_new_with_type (type=<optimized out>) at qom/object.c:714
  #5  0x000055a878c18399 in object_new (typename=typename@entry=0x55a878dec36a "isa-pit") at qom/object.c:747
  #6  0x000055a878cc8146 in qdev_new (name=name@entry=0x55a878dec36a "isa-pit") at hw/core/qdev.c:153
  #7  0x000055a878a8b439 in isa_new (name=name@entry=0x55a878dec36a "isa-pit") at hw/isa/isa-bus.c:160
  #8  0x000055a878adb782 in i8254_pit_init (base=64, isa_irq=0, alt_irq=0x0, bus=0x55a87ab38760) at include/hw/timer/i8254.h:54
  #9  microvm_devices_init (mms=0x55a87ac36800) at hw/i386/microvm.c:263
  #10 microvm_machine_state_init (machine=<optimized out>) at hw/i386/microvm.c:471
  #11 0x000055a878a944ab in machine_run_board_init (machine=machine@entry=0x55a87ac36800) at hw/core/machine.c:1239

The "isa-pit" type (TYPE_I8254) is missing. Add it.

Fixes: 0ebf007 ("hw/i386: Introduce the microvm machine type")
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20210616204328.2611406-24-philmd@redhat.com>

hw/i386/Kconfig

@@ -111,6 +111,7 @@ config MICROVM
     select ACPI_HW_REDUCED
     select PCI_EXPRESS_GENERIC_BRIDGE
     select USB_XHCI_SYSBUS
+    select I8254
 
 config X86_IOMMU
     bool