kernel: switch crc32 implementation back to default

kernel: switch crc32 implementation back to default

Commit ec885796c05a switched the crc32 implementation from default to
byte-at-a-time algorithm, which runs slower but consumes less memory.
A decade has passed, and we have already abandoned targets that had
small memory, so switch it back to default for faster speed.

Signed-off-by: Qingfang Deng <qingfang.deng@siflower.com.cn>