gptimer: support RC_FAST clock source

GPTimer on C6 supports RC_FAST as the clock source. The benefit of this
clock is that, the clock can sustain in light sleep.

Added a new API to return the real resolution of the timer handle.

examples/peripherals/.build-test-rules.yml

@@ -183,12 +183,6 @@ examples/peripherals/timer_group/gptimer_capture_hc_sr04:
   disable:
     - if: SOC_TIMER_SUPPORT_ETM != 1
 
-examples/peripherals/timer_group/legacy_driver:
-  disable_test:
-    - if: IDF_TARGET == "esp32c6"
-      temporary: true
-      reason: target esp32c6 is not supported yet
-
 examples/peripherals/touch_sensor:
   disable:
     - if: SOC_TOUCH_SENSOR_SUPPORTED != 1

examples/peripherals/timer_group/legacy_driver/pytest_timer_group.py

@@ -6,7 +6,6 @@ from pytest_embedded import Dut
 
 
 @pytest.mark.supported_targets
-@pytest.mark.temp_skip_ci(targets=['esp32c6'], reason='test failed')
 @pytest.mark.generic
 def test_timer_group_example(dut: Dut) -> None:
     dut.expect(r'Init timer with auto-reload', timeout=5)