spapr/xive: Mask the EAS when allocating an IRQ

spapr/xive: Mask the EAS when allocating an IRQ

If an IRQ is allocated and not configured, such as a MSI requested by
a PCI driver, it can be saved in its default state and possibly later
on restored using the same state. If not initially MASKED, KVM will
try to find a matching priority/target tuple for the interrupt and
fail to restore the VM because 0/0 is not a valid target.

When allocating a IRQ number, the EAS should be set to a sane default :
VALID and MASKED.

Reported-by: Satheesh Rajendran <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>
Message-Id: <20190813164420[email protected]>
Signed-off-by: David Gibson <[email protected]>