lib/crc: Use underlying functions instead of crypto_simd_usable()

lib/crc: Use underlying functions instead of crypto_simd_usable()

Since crc_kunit now tests the fallback code paths without using
crypto_simd_disabled_for_test, make the CRC code just use the underlying
may_use_simd() and irq_fpu_usable() functions directly instead of
crypto_simd_usable().  This eliminates an unnecessary layer.

Take the opportunity to add likely() and unlikely() annotations as well.

Link: https://lore.kernel.org/r/20250811182631.376302-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>