UPSTREAM: coresight: platform: Refactor graph endpoint parsing

Refactor the of graph endpoint parsing code, to make the error
handling easier.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(Upstream commit 6575fdb74645c14453f3119568ec45cbc54d4afb).

Bug: 140266694
Change-Id: If271717bc321a90eb9dfaa40c3a187395991f931
Signed-off-by: Yabin Cui <yabinc@google.com>