irqchip: vt8500: Staticize local symbols

This driver is converted to use IRQCHIP_DECLARE and irqchip_init.
vt8500_handle_irq() and vt8500_irq_init() are only referenced in this file, so
make them static.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Cc: Olof Johansson <olof@lixom.net>
Link: http://lkml.kernel.org/r/1372995229.4038.1.camel@phoenix
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>