This option enables the user to select the secure hash algorithm
to be used for generating the hash. It supports the following
options:
    - sha256 (default)
    - sha384
    - sha512

Change-Id: Icb093cec1b5715e248c3d1c3749a2479a7ab4b89
Signed-off-by: Qixiang Xu <qixiang.xu@arm.com>