1. Move mpp_log.h to inc for external user.
2. Add mpp_debug.h for mpp internal logging.
3. Fix some warning.
4. Add log level setup function.
5. Check env log_level value in mpp_get_log_level call.
NOTE:
1. mpp internal module should use mpp_debug.h and mpp external user
should use mpp_log.h
2. Use mpp_get_log_level to update mpp_log_level when the env changed.
Change-Id: I90a55a02a72db177533013280dfe111ca3479229
Signed-off-by: Herman Chen <herman.chen@rock-chips.com>
