rtc_clk_apll_enable() function

Enable or disable APLL Output frequency is given by the formula: apll_freq = xtal_freq * (4 + sdm2 + sdm1/256 + sdm0/65536)/((o_div + 2) * 2) The dividend in this expression should be in the range of 240 - 600 MHz. In rev. 0 of ESP32, sdm0 and sdm1 are unused and always set to 0.