Docs: Update Storage integration guides

Updates the ITS and PS integration guides to cover the new HAL APIs and
related changes. Removes the ITS and PS sections in the platform readme
as it only duplicated information in the integration guide, which is the
more logical place for service-related documentation.

Change-Id: I1e4e1778b9a3eae21a63ddb969d4187e53e4517f
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
3 files changed