irqchip: crossbar: Check for premapped crossbar before allocating

If irq_of_parse_and_map is executed twice, the same crossbar is mapped to two
different GIC interrupts. This is completely undesirable. Instead, check
if the requested crossbar event is pre-allocated and provide that GIC
mapping back to caller if already allocated.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Sricharan R <r.sricharan@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Link: https://lkml.kernel.org/r/1403766634-18543-3-git-send-email-r.sricharan@ti.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

diff --cc drivers/irqchip/irq-crossbar.c
Simple merge