Remove rom start/size macros when bootloader=true
Remove rom start/size macros when bootloader=true

Allow the application to specify this depending on whether/how
it is using the bootloader and whether it requires a CM0+ image.

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