lib: Allow crc16 code to be dropped

lib: Allow crc16 code to be dropped

This code is not necessarily needed in VPL, even if SPL uses it, so
adjust the rules to allow it to be dropped.

Do the same for the hash API.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>