common: allow rma_auth to work with both crypto and dcrypto
common: allow rma_auth to work with both crypto and dcrypto

On Cr50 the crypto library has a slightly different API, as indicated
by the presence of the CONFIG_DCRYPTO configuration option.

This patch provides a wrapper which allows to calculate a SHA256 HMAC
hash using either underlying crypto API.

BRANCH=cr50
BUG=b:37952913
TEST=make buildall -j

Change-Id: Ibb8c60e50139fd5506a4dd5f2ed19653c68af8cb
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/690440
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec