drivers: pwm: ledc: esp32: Fix RC_FAST and REF_TICK

Depending on clock config init, some devices might be initialized
with RC_FAST clock enabled but not calibrated. Logic to detect if
clock is calibrated was fixed for this reason. Also, logic to set
RC_FAST and REF_TICK for devices with timer specific clocks (ESP32
and ESP32-S2) was also fixed.

Signed-off-by: Raffael Rostagno <raffael.rostagno@espressif.com>