docs(auth): add 'calc_hash' function's details in CM

Updated the Crypto Module section to detail the 'calc_hash'
function.

Change-Id: I04a24abba150745e4eba6273bdb7cf12b66bfebc
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
1 file changed