kcsan: Remove kcsan_report_type

Now that the reporting code has been refactored, it's clear by
construction that print_report() can only be passed
KCSAN_REPORT_RACE_SIGNAL or KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, and these
can also be distinguished by the presence of `other_info`.

Let's simplify things and remove the report type enum, and instead let's
check `other_info` to distinguish these cases. This allows us to remove
code for cases which are impossible and generally makes the code simpler.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[ elver@google.com: add updated comments to kcsan_report_*() functions ]
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>