Add resource management for serial for the NRF52 family
Add resource management for serial for the NRF52 family

Instance counter keeps track of how many objects have been
initialized and freed. On the first object the instance is
enabled and on the last object the instance is disabled.

betzw/mbed-os,c1728p9/mbed-os,betzw/mbed-os,mbedmicro/mbed,andcor02/mbed-os,c1728p9/mbed-os,betzw/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,betzw/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,c1728p9/mbed-os,betzw/mbed-os,betzw/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,andcor02/mbed-os