sh: Rename cpuidle states to fit general conventions

C0 is known as "busy", "not idle" state.
X86 "busy polling" state also got renamed from C0
to "POLL" recently.
Let's stay consistent with naming to avoid confusions.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>