target/ppc: Don't clobber MSR:EE on PM instructions

target/ppc: Don't clobber MSR:EE on PM instructions

When issuing a power management instruction, we set MSR:EE
to force ppc_hw_interrupt() into calling powerpc_excp()
to deal with the fact that on P7 and P8, the system reset
caused by the wakeup needs to be generated regardless of
the MSR:EE value (using LPCR only).

This however means that the OS will see a bogus SRR1:EE
value which is a problem. It also prevents properly
implementing P9 STOP "light".

So fix this by instead putting some logic in ppc_hw_interrupt()
to decide whether to deliver or not by taking into account the
fact that we are waking up from sleep.

The LPCR isn't checked as this is done in the has_work() test.

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: <20190215161648.9600-3-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>