1. add some efuse api to get rtc & digital voltage
2. set dig_rtc voltage to a fix value storing in efuse no mater which cpu frequency
3. modify hardware code in bootloader to fit all c3 ECO3 version
1. deepsleep poweron reset bug in high temperature before ECO3;
2. brownout reset bug before ECO2;
3. bbpll voltage low bug before ECO3;
4. need xpd iph for xtal before ECO3;