Compile pckbd only once

Use a qemu_irq to indicate A20 line changes. Move I/O port 92
to pckbd.c.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/default-configs/mips64-softmmu.mak b/default-configs/mips64-softmmu.mak
index dfd30db..21338ff 100644
--- a/default-configs/mips64-softmmu.mak
+++ b/default-configs/mips64-softmmu.mak
@@ -10,6 +10,7 @@
 CONFIG_PARALLEL=y
 CONFIG_I8254=y
 CONFIG_PCSPK=y
+CONFIG_PCKBD=y
 CONFIG_USB_UHCI=y
 CONFIG_FDC=y
 CONFIG_ACPI=y