cuda: set timer 1 frequency property to CUDA_TIMER_FREQ

cuda: set timer 1 frequency property to CUDA_TIMER_FREQ

Now that we have successfully decoupled the timebase frequency and the hardware
timer frequency, set the timer 1 frequency property to CUDA_TIMER_FREQ and alter
get_next_irq_time() to use it rather than the hard-coded constant.

In addition to this we must now switch the tb_diff calculation over to use the
timebase frequency now that the hardware clock frequency and the timebase
frequency are different.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
[dwg: Correct a conflict due to a bug in an earlier patch]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>