MIPS: JZ4740: Cleanup the mechanical irq_chip conversion

The conversion did not make use of the new chip flag which signals the
core code to mask the chip before calling the set_type callback. Sigh.
Use the new lockdep helper as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2183/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>