tests/basic: mark CFB and CFB8 as stream block cipher modes

* tests/basic.c (get_algo_mode_blklen): Return '1' for CFB and CFB8.

This commit marks CFB and CFB8 modes as stream ciphers so that they get
run through tests/basic.c's split input buffer testing (input split&feed
to cipher in variating sized parts).

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>