powerpc/xive: Rename XIVE_IRQ_NO_EOI to show its a flag

This is a simple cleanup to identify easily all flags of the XIVE
interrupt structure. The interrupts flagged with XIVE_IRQ_FLAG_NO_EOI
are the escalations used to wake up vCPUs in KVM. They are handled
very differently from the rest.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201210171450.1933725-3-clg@kaod.org