irqchip/gic-v4: Fix building with ancient gcc

gcc-4.5 and earlier don't like named initializers for anonymous
union members:

drivers/irqchip/irq-gic-v4.c: In function 'its_map_vlpi':
drivers/irqchip/irq-gic-v4.c:176:3: error: unknown field 'map' specified in initializer
drivers/irqchip/irq-gic-v4.c:176:3: error: missing braces around initializer
drivers/irqchip/irq-gic-v4.c:176:3: error: (near initialization for 'info.<anonymous>')
drivers/irqchip/irq-gic-v4.c: In function 'its_get_vlpi':
drivers/irqchip/irq-gic-v4.c:192:3: error: unknown field 'map' specified in initializer
drivers/irqchip/irq-gic-v4.c:192:3: error: missing braces around initializer
drivers/irqchip/irq-gic-v4.c:192:3: error: (near initialization for 'info.<anonymous>')
drivers/irqchip/irq-gic-v4.c: In function 'its_prop_update_vlpi':
drivers/irqchip/irq-gic-v4.c:208:3: error: unknown field 'config' specified in initializer
drivers/irqchip/irq-gic-v4.c:208:3: error: missing braces around initializer
drivers/irqchip/irq-gic-v4.c:208:3: error: (near initialization for 'info.<anonymous>')
drivers/irqchip/irq-gic-v4.c:208:3: error: initialization makes pointer from integer without a cast

This is fairly easy to work around, by using extra curly braces.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>