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/ppc-softmmu.mak b/default-configs/ppc-softmmu.mak
index 958bf75..03cc20f 100644
--- a/default-configs/ppc-softmmu.mak
+++ b/default-configs/ppc-softmmu.mak
@@ -8,6 +8,7 @@
 CONFIG_VGA_PCI=y
 CONFIG_SERIAL=y
 CONFIG_I8254=y
+CONFIG_PCKBD=y
 CONFIG_FDC=y
 CONFIG_OPENPIC=y
 CONFIG_PREP_PCI=y