powerpc/ipic: Support edge on IRQ0

External IRQ0 (index 48) has the same capabilities as the other IRQ1-7
and is handled by the same register IPIC_SEPNR. When this register is
not specified for "ack" in "ipic_info", you cannot configure this IRQ
as IRQ_TYPE_EDGE_FALLING. This oversight was probably due to the
non-contiguous hwirq numbering of IRQ0 in the IPIC.

Signed-off-by: Jurgen Schindele <schindele@nentec.de>
[scottwood: Cleaned up commit message and posted as a proper patch]
Signed-off-by: Scott Wood <oss@buserror.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/ipic.c

@@ -315,6 +315,7 @@ static struct ipic_info ipic_info[] = {
 		.prio_mask = 7,
 	},
 	[48] = {
+		.ack	= IPIC_SEPNR,
 		.mask	= IPIC_SEMSR,
 		.prio	= IPIC_SMPRR_A,
 		.force	= IPIC_SEFCR,