The implementation of FW_LOADER requires CMDLINE to be enabled, and
expressses this. In order to not have to have every users also depends
on CMDLINE introduce SUPPORTS_FW_LOADER. This depends on CMDLINE and
ENV_SUPPORT and then we have all users depends on SUPPORTS_FW_LOADER.
Signed-off-by: Tom Rini <trini@konsulko.com>