softirq: Don't defer all softirq during RT task

Since 'commit f332a9d53e33 ("softirq: defer softirq processing to
ksoftirqd if CPU is busy with RT")', all softirqs are deferred
to ksoftirqd if one of the potentially long softirqs are pending.
This can significantly delay processing of tasklets and timers,
which are frequently designed to be running at high priority.

Defer only the potentially slow softirqs to ksoftirqd.

Change-Id: I7a2ef7c59749ccf086066c59962ff326786da6f4
Signed-off-by: Björn Davidsson <bjorn.davidsson@sony.com>
[clingutla@codeaurora.org: Renamed local variables and refactored
deferred logic to macro for avoiding potential deadlock.]
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>