powerpc: mpic: Cleanup flow type handling

The core irq_set_type() function updates the flow type when the chip
callback returns 0. So setting the type is bogus.

The new core code allows to update the type in irq_data and return
IRQ_SET_MASK_OK_NOCOPY, so the core code will not touch it, except for
setting the IRQ_LEVEL flag.

Retrieve the IRQ_LEVEL information from irq_data which avoids a
redundant sparse irq lookup as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>