lib/crypto: sha: Update Kconfig help for SHA1 and SHA256

Update the help text for CRYPTO_LIB_SHA1 and CRYPTO_LIB_SHA256 to
reflect the addition of HMAC support, and to be consistent with
CRYPTO_LIB_SHA512.

Link: https://lore.kernel.org/r/20250731224218.137947-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>