ARM: LPC32xx: Relocate calls to irq_set_chained_handler()

This patch fixes the issue of an access to a yet uninitialized data structure
at the point where irq_set_chained_handler() was called by moving the
respective calls to the end of lpc32xx_init_irq().

The call path was:

irq_set_chained_handler()
-> __irq_set_handler()
-> irq_startup()
-> irq_enable()
-> desc->irq_data.chip->irq_unmask()

at which point lpc32xx_unmask_irq() effectively read desc->irq_data.hwirq which
was only later initialized.

Signed-off-by: Roland Stigge <stigge@antcom.de>