linker script: should not be under misc in tools

[0xc0170]

I misplaced linker script in one of the records, and it failed to produce correct path (relative to the generated project):

correct:

tool_specific:
    gcc_arm:
        linker_file:
            - cmsis/MK64F12/MK64F12.ld

incorrect but no error:

tool_specific:
    gcc_arm:
        misc:
            linker_file:
                - cmsis/MK64F12/MK64F12.ld