time: Fix get_ticks being non-monotonic

get_ticks does not always succeed. Sometimes it can be called before the
timer has been initialized. If it does, it returns a negative errno.
This causes the timer to appear non-monotonic, because the value will
become much smaller after the timer is initialized.

No users of get_ticks which I checked handle errors of this kind. Further,
functions like tick_to_time mangle the result of get_ticks, making it very
unlikely that one could check for an error without suggesting a patch such
as this one.

This patch panics if we ever get an error. There are two cases in which
this can occur. The first is if we couldn't find/probe the timer for some
reason. One reason for this is if the timer is not available so early. This
likely indicates misconfiguration. Another reason is that the timer has an
invalid/missing device tree binding. In this case, panicing is also
correct. The second case covers errors calling get_count. This can only
occur if the timer is missing a get_count function (or on RISC-V, but that
should be fixed soon).

Fixes: c8a7ba9e
Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>