This updates the minimal supported version of CMake to 3.16, which in turn enables us to use more CMake features and have a cleaner build system.
This is the version that provides most new features and also the one we use in our latest docker image for CI.
Moved the following kconfig options out of the target component:
* CONFIG_ESP*_DEFAULT_CPU_FREQ* -> esp_system
* ESP*_REV_MIN -> esp_hw_support
* ESP*_TIME_SYSCALL -> newlib
* ESP*_RTC_* -> esp_hw_support
Where applicable these target specific konfig names were merged into
a single common config, e.g;
CONFIG_ESP*_DEFAULT_CPU_FREQ -> CONFIG_ESP_DEFAULT_CPU_FREQ_MHZ
