periph_rtc_apll_freq_set() function

- ESP_OK: APLL frequency set success - ESP_ERR_INVALID_ARG: The input expt_freq is out of APLL support range - ESP_ERR_INVALID_STATE: APLL is refered by more than one peripherals, not allowed to change its frequency now

Have to call 'periph_rtc_apll_acquire' to enable APLL power before setting frequency This calculation is based on the inequality: xtal_freq * (4 + sdm2 + sdm1/256 + sdm0/65536) >= CLK_LL_APLL_MULTIPLIER_MIN_HZ(350 MHz) It will always calculate the minimum coefficients that can satisfy the inequality above, instead of loop them one by one. which means more appropriate coefficients are likely to exist. But this algorithm can meet almost all the cases and the accuracy can be guaranteed as well. The APLL frequency is only allowed to set when there is only one peripheral refer to it. If APLL is already set by another peripheral, this function will return `ESP_ERR_INVALID_STATE` and output the current frequency by parameter `real_freq`.