crypto,fs: Separate out hkdf_extract() and hkdf_expand()

Separate out the HKDF functions into a separate module to
to make them available to other callers.
And add a testsuite to the module with tes

crypto,fs: Separate out hkdf_extract() and hkdf_expand()

Separate out the HKDF functions into a separate module to
to make them available to other callers.
And add a testsuite to the module with test vectors
from RFC 5869 (and additional vectors for SHA384 and SHA512)
to ensure the integrity of the algorithm.

Signed-off-by: Hannes Reinecke <[email protected]>
Acked-by: Eric Biggers <[email protected]>
Acked-by: Herbert Xu <[email protected]>
Signed-off-by: Keith Busch <[email protected]>

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