[MIPS] Jazz: disable PIT; cleanup R4030 clockevent

Fix ISA irq acknowledge.
Make r4030 clockevent code look like other mips clockevent code.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>