Use standard errno definitions in load_auth_image()

Use standard errno definitions in load_auth_image()

This patch replaces custom definitions used as return values for
the load_auth_image() function with standard error codes defined
in errno.h. The custom definitions have been removed.

It also replaces the usage of IO framework error custom definitions,
which have been deprecated. Standard errno definitions are used
instead.

Change-Id: I1228477346d3876151c05b470d9669c37fd231be