coresight: Use enum type for cs_mode wherever possible

mode is stored as a local_t, but it is also passed around a lot as a
plain u32, so use the correct type wherever local_t isn't currently
used. This helps a little bit with readability.

Reviewed-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230425143542.2305069-3-james.clark@arm.com