target-ppc: Use interrupts for escc

target-ppc: Use interrupts for escc

When using the escc with Linux, we need interrupts. So instead of creating
a dummy device, let's just map them to the openpic we have anyways.

This makes Linux on PPC64 with console=ttyPZ0 work.

Obviously, this change needs to be reflected in openbios. Patch for that
follows this one. Please update the binary then.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>