MIPS: TXx9: micro optimization for clocksource and clock_event

Use container structure for clocksource, clock_event_device and hold a
pointer to txx9_tmr_reg in it.

This saves a few instructions in clocksource and clock_event handlers.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>