service: fix and refactor atomic service accesses

service: fix and refactor atomic service accesses

This commit fixes an issue in the service runner function,
where the atomic value was not cleared on exiting the service
function. This resulted in future attempts to run the service
to appear like the function was running, however it was in
reality deadlocked.

This commit refactors the atomic handling to be more readable,
by splitting the implementation code into a new static inline
function. The remaining flow control of atomics in the existing
function is refactored for readability.

Fixes: 21698354c832 ("service: introduce service cores concept")

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>