smp: Inline on_each_cpu_cond() and on_each_cpu()

Simplify the code and avoid having an additional function on the stack
by inlining on_each_cpu_cond() and on_each_cpu().

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
[ Minor edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210220231712.2475218-10-namit@vmware.com