scripts: only generate config from feature flag if fully match

scripts: only generate config from feature flag if fully match

Without this change the code checked if the string was contained in the
feature option and not if the string matches the complete word. This only
removes the nand option from the omap24xx target, the other changes are
only removing options which were added twice.

Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>