coresight: make 'coresight-name' a required property

Without 'coresight-name' a CoreSight device gets registered with its
dev_name.

This can be a problem in case where we have CoreSight properties defined
within some other platform device.

Make 'coresight-name' a required property for a CoreSight device to
avoid this problem.

Change-Id: I5e192c4d850bb040983024cfe163714fbebbb199
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>