target/ppc: Fix support for "STOP light" states on POWER9

target/ppc: Fix support for "STOP light" states on POWER9

STOP must act differently based on PSSCR:EC on POWER9. When set, it
acts like the P7/P8 power management instructions and wake up at 0x100
based on the wakeup conditions in LPCR.

When PSSCR:EC is clear however it will wakeup at the next instruction
after STOP (if EE is clear) or take the corresponding interrupts (if
EE is set).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20190215161648.9600-4-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>