crypto: blake2b - add blake2b generic implementation

The patch brings support of several BLAKE2 variants (2b with various
digest lengths).  The keyed digest is supported, using tfm->setkey call.
The in-tree user will be btrfs (for checksumming), we're going to use
the BLAKE2b-256 variant.

The code is reference implementation taken from the official sources and
modified in terms of kernel coding style (whitespace, comments, uintXX_t
-> uXX types, removed unused prototypes and #ifdefs, removed testing
code, changed secure_zero_memory -> memzero_explicit, used own helpers
for unaligned reads/writes and rotations).

Further changes removed sanity checks of key length or output size,
these values are verified in the crypto API callbacks or hardcoded in
shash_alg and not exposed to users.

Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Makefile

@@ -74,6 +74,7 @@ obj-$(CONFIG_CRYPTO_STREEBOG) += streebog_generic.o
 obj-$(CONFIG_CRYPTO_WP512) += wp512.o
 CFLAGS_wp512.o := $(call cc-option,-fno-schedule-insns)  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79149
 obj-$(CONFIG_CRYPTO_TGR192) += tgr192.o
+obj-$(CONFIG_CRYPTO_BLAKE2B) += blake2b_generic.o
 obj-$(CONFIG_CRYPTO_GF128MUL) += gf128mul.o
 obj-$(CONFIG_CRYPTO_ECB) += ecb.o
 obj-$(CONFIG_CRYPTO_CBC) += cbc.o