Contribution description

This PR adds a simple implementation of _gettimeofday_r based on the microsecond system timer (system_get_time_64()) without occupying a `TIMER_DEV.

Since PR #18027, the ESP32 port uses the module libc_gettimeofday by default which enables implicitly modules xtimer and ztimer_usec which in turn occupies TIMER_DEV(0).

The changes in this PR

• allow to remove this dependency on module libc_gettimeofday.
• fix the execution error in tests/periph_timer due to TIMER_DEV(0) is ocu

In this implementation, the the microsecond system timer is realized on top of a peripheral timer. In future implementations of the ESP32 port, the microsecond hardware system timer will be used for that purpose.

Testing procedure

1. Check the used modules list:

    BOARD=esp32-wroom-32 make -C tests/shell info-modules
   

   Without this PR the module list is:

   ...
   
   tsrb
   xtensa 
   xtimer
   ztimer
   ztimer64
   ztimer64_init
   ztimer64_usec
   ztimer64_xtimer_compat
   ztimer_convert
   ztimer_convert_frac
   ztimer_convert_shift
   ztimer_core
   ztimer_extend
   ztimer_init
   ztimer_periph_timer
   ztimer_usec
   ztimer_xtimer_compat
   

   With this PR the module list should be:

   ...
   tsrb
   xtensa
   

2. Flash an test

    BOARD=esp32-wroom-32 make -C tests/periph_timer`
   

   Without this PR the output is:

   Test for peripheral TIMERs
   Available timers: 3
   
   Testing TIMER_0:
   TIMER_0: ERROR on initialization - skipping
   ...
   TEST FAILED
   

   With this PR the output should be:

   Test for peripheral TIMERs
   Available timers: 3
   
   Testing TIMER_0:
   TIMER_0: initialization successful
   ...
   TEST SUCCEEDED
   

Issues/PRs references

Found in test runs in CI for #16833