Add a helper function `__should_generate_sdkconfig()` that checks
whether the sdkconfig file should be generated. The
`__generate_sdkconfig()` function can be called multiple times, such as
when the initial sdkconfig is generated at the start of the build
process and later after additional components are fetched by the
component manager. There might be no components fetched by the
component manager, for example, in the hello_world example, or the
downloaded components may not contain any configuration files. In such
cases, there is no need to regenerate the sdkconfig. This helper
function stores the list of configuration files in the
`__PREV_KCONFIGS`, `__PREV_KCONFIG_PROJBUILDS`, and
`__PREV_SDKCONFIG_RENAMES` build properties at its end, and at the
beginning, it compares them with the current lists of configuration
files.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>