Add the attribute flash to enable priority inheritance and robust mode.
The robust flag allows mutexes held by terminated threads to be
properly released.
Build jobs are failing due build error "arm_hal_timer.cpp:50:5:
error: reference to 'callback' is ambiguous".
Fix the build error by renaming callback to arm_hal_callback to
avoid collision with callback defined in ./mbed-os/hal/api/Callback.h
Move the library files used by both nanostack and client into a common
location. This allows both client and nanostack to be built stand-alone.
The patch moves the following libraries into a common location:
-mbed-client-c
-mbed-client-randlib
-mbed-trace
-nanostack-hal-mbed-cmsis-rtos
-nanostack-libservice
-sal-stack-nanostack-eventloop
And moves the library 'coap-service' from client into nanostack.