target/ppc: Fix pending HDEC when entering PM state

target/ppc: Fix pending HDEC when entering PM state

HDEC is defined to not wake from PM state. There is a check in the HDEC
timer to avoid setting the interrupt if we are in a PM state, but no
check on PM entry to lower HDEC if it already fired. This can cause a
HDECR wake up and  QEMU abort with unsupported exception in Power Save
mode.

Fixes: 4b236b621bf ("ppc: Initial HDEC support")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-ID: <20230726182230.433945-4-npiggin@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>