kconfig.py: Use messages returned by load_config() and write_config()
kconfig.py: Use messages returned by load_config() and write_config()

load_config() and write_config() now return a message to print. This
message also says whether the configuration was loaded (replace=True) or
merged (replace=False), and whether the new .config is different from
the old (for write_config()).

Print the returned messages and remove some old print()s.

Also switch to an improved warning control API (the old one is still
supported, but might as well).

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

Vudentz/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr