hw/mips/Kconfig: Malta machine requires the pcnet network card

This fixes when configuring with --without-default-devices:

  $ qemu-system-mips64 -bios /dev/null -M malta
  qemu-system-mips64: Unsupported NIC model: pcnet

Fixes: 7c28b92
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190316200818.8265-7-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

default-configs/mips-softmmu-common.mak

@@ -35,6 +35,7 @@ CONFIG_MIPS_CPS=y
 CONFIG_MIPS_ITU=y
 CONFIG_R4K=y
 CONFIG_MALTA=y
+CONFIG_PCNET_PCI=y
 CONFIG_MIPSSIM=y
 CONFIG_ACPI_SMBUS=y
 CONFIG_SMBUS_EEPROM=y