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
update all struct headers to be more "standardized":
- bit fields are properly wrapped with struct
- bitwidth sum should be 32 within same struct, so that it's correctly padded with reserved bits
- bit field should be uint32_t
- typedef volatile struct xxx{} yyy;: xxx must exists. refer: https://github.com/espressif/esp-idf/pull/3199
added helper macros to force peripheral registers being accessed in 32 bitwidth
added a check script into ci
