target/ppc: Implement new wait variants

target/ppc: Implement new wait variants

ISA v2.06 adds new variations of wait, specified by the WC field. These
are not all compatible with the prior wait implementation, because they
add additional conditions that cause the processor to resume, which can
cause software to hang or run very slowly.

At this moment, with the current wait implementation and a pseries guest
using mainline kernel with new wait upcodes [1], QEMU hangs during boot if
more than one CPU is present:

 qemu-system-ppc64 -M pseries,x-vof=on -cpu POWER10 -smp 2 -nographic
-kernel zImage.pseries -no-reboot

QEMU will exit (as there's no filesystem) if the test "passes", or hang
during boot if it hits the bug.

ISA v3.0 changed the wait opcode and removed the new variants (retaining
the WC field but making non-zero values reserved).

ISA v3.1 added new WC values to the new wait opcode, and added a PL
field.

This patch implements the new wait encoding and supports WC variants
with no-op implementations, which provides basic correctness as
explained in comments.

[1] https://lore.kernel.org/all/20220720132132.903462-1-npiggin@gmail.com/

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Tested-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220720133352.904263-1-npiggin@gmail.com>
[danielhb: added information about the bug being fixed]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>