cpu/esp32: fix dependency for periph/rtt and module esp_rtc_timer_32k

[gschorcht]

Contribution description

This PR is a split-off from PR #17844, which provides a fix of module dependency for periph_rtt.

If the ESP32 has an external 32k crystal connected, the clock from this crystal should be used for the RTT peripheral and not only for the RTC peripheral. Since the ESP32 RTC implementation uses RTT on top of RTT (module rtc_rtt), with this change the 32k crystal will be used for both RTT and RTC if present.

Testing procedure

1. Use command:

   BOARD=esp32-wrover-kit make -j8 -C tests/periph_rtt info-modules | grep esp_rtc_timer_32k
   BOARD=esp32-wroom-32 make -j8 -C tests/periph_rtt info-modules | grep esp_rtc_timer_32k
   

   Module esp_rtc_timer_32k is used for board esp32-wrover-kit but not for board esp32-wroom-32 with this PR. Without this PR it is not used at all.

2. Use command:

   TEST_KCONFIG=1 BOARD=esp32-wrover-kit make -j8 -C tests/periph_rtc info-modules | grep esp_rtc_timer_32k
   TEST_KCONFIG=1 BOARD=esp32-wroom-32 make -j8 -C tests/periph_rtc info-modules | grep esp_rtc_timer_32k
   

   Module esp_rtc_timer_32k is used for board esp32-wrover-kit but not for board esp32-wroom-32 with this PR. Without this PR it is not used at all.

3. Use command:

   BOARD=esp32-wrover-kit make -j8 -C tests/periph_rtc info-modules | grep esp_rtc_timer_32k
   BOARD=esp32-wroom-32 make -j8 -C tests/periph_rtc info-modules | grep esp_rtc_timer_32k
   

   Module esp_rtc_timer_32k is still used for board esp32-wrover-kit but not for board esp32-wroom-32 with this PR.

4. Compile and flash tests/periph_rtt for any ESP32 board that has connected an external 32k crystal:

   BOARD=esp32-wrover-kit make -j8 -C tests/periph_rtc flash term
   

   The test should still work with this change.

Issues/PRs references

Split-off from PR #17844

[gschorcht]

@benpicco Thanks for reviewing and merging.