When creating G0 layer, some regi2c_*.h headers were moved out from
esp_hw_support (G1) to soc (G0). In order to be consistent with that change,
move all the remaining regi2c_*.h headers to soc too.
1. Clean up clk usage in IDF, replace rtc_clk_xtal/apb_freq_get with
upper level API esp_clk_xtal/apb_freq
2. Fix small errors and wrong comments related to clock
3. Add clk_tree_defs.h to provide an unified clock id for each chip
Modify the NGed drivers to adopt new clock ids
