Exynos: Change get_timer() to work correctly

Exynos: Change get_timer() to work correctly

At present get_timer() does not return sane values. It should count up
smoothly in milliscond intervals.

We can change the PWM to count down at 1MHz, providing a resolution
of 1us and a range of about an hour between required get_timer() calls.

Test with command "sf probe 1:0; time sf read 40008000 0 1000".
Try with different numbers of bytes and see that sane values are obtained

Signed-off-by: Simon Glass <[email protected]>
Signed-off-by: Akshay Saraswat <[email protected]>
Acked-by: Simon Glass <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>