ARM: imx5: tzic_init_irq() can directly be .init_irq hook

After i.MX51 supports DT only, tzic_init_irq() can figure out the
tzic_base on its own.  Thus, it can directly be .init_irq hook, and
mx51[53]_init_irq() can be saved.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>