coresight: Fail to open with return stacks if they are unavailable

Maintain consistency with the other options by failing to open when they
aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
requested but not supported by hardware.

The consequence of not doing this is that the user may not be
aware that they are not enabling the feature as it is silently disabled.

Signed-off-by: James Clark <james.clark@arm.com>