Revert "Temporarily remove NUCLEO_F401RE support"

This reverts commit 6c96b73af64afe05693b72e02e04f0a6f1340483.

Re-enable NUCLEO_F401RE support in the working branch.
Added NUCLEO_F411RE option.

1. Tested with NUCLEO-F411RE board.
2. Tested samples : HelloWorld
Updated NUCLEO-F411RE makefile for new mbed SDK

The device specific makefiles now require a different format after the
latest mbed SDK and GCC4MBED updates.  I made the necessary changes in
this commit.