Summary of changes:
- bootloader_clock split into *_clock_init and *_clock_loader.
Only esp_clk_apb_freq is in *_clock_loader.
- bootloader_common moved out of loader; functions needed in loader
(or, referenced from bootloader_utility) were moved into
bootloader_common_loader.c.
- assert and abort moved into bootloader_panic, made part of the
loader
- rtc_clk and rtc_time made part of loader
