Start implementing pSeries logical partition machine

This patch adds a "pseries" machine to qemu.  This aims to emulate a
logical partition on an IBM pSeries machine, compliant to the
"PowerPC Architecture Platform Requirements" (PAPR) document.

This initial version is quite limited, it implements a basic machine
and PAPR hypercall emulation.  So far only one hypercall is present -
H_PUT_TERM_CHAR - so that a (write-only) console is available.

Multiple CPUs are permitted, with SMP entry handled kexec() style.

The machine so far more resembles an old POWER4 style "full system
partition" rather than a modern LPAR, in that the guest manages the
page tables directly, rather than via hypercalls.

The machine requires qemu to be configured with --enable-fdt.  The
machine can (so far) only be booted with -kernel - i.e. no partition
firmware is provided.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
