Add support for SHA384 and SHA512

Add support for SHA384 and SHA512

The current recommendation for best security practice from the US government
is to use SHA384 for TOP SECRET [1].

This patch adds support for SHA384 and SHA512 in the hash command, and also
allows FIT images to be hashed with these algorithms, and signed with
sha384,rsaXXXX and sha512,rsaXXXX

The SHA implementation is adapted from the linux kernel implementation.

[1] Commercial National Security Algorithm Suite
http://www.iad.gov/iad/programs/iad-initiatives/cnsa-suite.cfm

Signed-off-by: Reuben Dowle <reuben.dowle@4rf.com>