sched: Add helper kstat_cpu_softirqs_sum()

mainline inclusion
from mainline-v6.3-rc1
commit 3ca0a6ea
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3ca0a6ea8f6de0f21a9331ff3596a9c073fbdab0



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Add a kstat_cpu_softirqs_sum() function that is similar to
kstat_cpu_irqs_sum(), but which counts software interrupts since boot
on the specified CPU.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Josh Don <joshdon@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>