esp32: ets_update_cpu_frequency should set tick scale for both CPUs
ets_update_cpu_frequency ROM function updates g_ticks_per_us, which is has two copies, one for each CPU.
The APP CPU copy of g_ticks_per_us never got updated, resulting in shorter delays produced by ets_delay_us on the APP CPU.
This MR replaces ROM ets_update_cpu_frequency with a copy in IRAM which updates scaling factors on both of the CPUs.
So now we get expected delays (in microseconds):
```
ets_delay_us core=0 expected=50000 actual=50014
ets_delay_us core=1 expected=50000 actual=50015
vTaskDelay core=0 expected=50000 actual=49428
vTaskDelay core=1 expected=50000 actual=50000
```
Reported on the forum: http://esp32.com/viewtopic.php?f=2&t=713#p3722
See merge request !373
4f909b8ecc