Adding variables that can be set from other linker scripts:
- _bootloader_head_size:
Bootloader flash offset in front of the application.
- _bootloader_tail_size:
Bootloader offset from the tail of the flash.
In case the bootloader is located at the end.
- _bootloader_head_ram_size:
Bootloader RAM usage in front of the application.
Updated calculations of application flash and RAM.