Toolchain GCC ARM for Nucleo_F411RE

- Linker script and startup for Nucleo_F411 - both are copies of
Nucleo_F401 with some changes (memory size, interrupt vector table)
- changes in target.py for the new toolchain
target extension of test: DigitalIn DigitalOut

Extension of the test 'DigitalIn DigitalOut' for Nucleo_F401RE and
Nucleo_F411RE
Merge pull request #484 from ohagendorf/master

[Nucleo_F4x1]: 2 extensions for a) toolchain ARM_GCC and b) test DigitalIn DigitalOut