coresight: only use etm0 for populating configuration

With maxcpus=1, only core0 will be running with other cores in
reset until they are explicitly hotplugged on. To avoid reading
ETM registers for cores that are in reset during probe, use only
ETM0 for populating configuration info. For other ETM probes,
copy the info from ETM0.

Change-Id: I9ae4539b004956a026e919323413f9e3c7d5ba4a
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>