Update mbed_rtx.h switch for new target naming
Update mbed_rtx.h switch for new target naming

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