1. add Makefile.nimble that helps integrate NimBLE with custom applications
To enable NimBLE for an custom application, user needs to include Makefile.nimble in the app's Makefile:
include $(APPDIR)/wireless/bluetooth/nimble/Makefile.nimble
2. add NuttX specific syscfg.h
- file based on nimble/porting/examples/nuttx/include/syscfg/syscfg.h
- all unnecessary definitions was removed
- definitions are configurable from Kconfig
3. add NuttX specific logcfg.h
- bind NimBLE logging with debug.h macros
