mips: Expire late timers when reading cp0_count

When reading cp0_count from a timer with a late trigger that should
already have expired, expire it and raise the timer irq.

This makes it possible for guest code (e.g, Linux) that first read
cp0_count, then compare it with cp0_compare and check for raised
timer interrupt lines to run reliably.

Acked-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
