If MICROPY_FROZEN_MANIFEST is set from the cmake command line, then it will override the default and any manifest set by the board.
This commit re-enables the command-line make option "FROZEN_MANIFEST". The boards/*/mpconfigboard.cmake will now use the command-line FROZEN_MANIFEST value if supplied. Usage: make FROZEN_MANIFEST=~/foo/my-manifest.py
Signed-off-by: Damien George <damien@micropython.org>