coresight: add support to read AUTHSTATUS

The status of the CoreSight fuses can be derived from the AUTHSTATUS
register. This patch add support to read AUTHSTATUS, which could be used
by Coresight device drivers to determine if that component is functional
in hardware.

Change-Id: I6b7ac2a3558c238ac5fca452ddfb6c88eef14b8b
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>