sparc idle: rename pm_idle to sparc_idle

(pm_idle)() is being removed from linux/pm.h
because Linux does not have such a cross-architecture concept.

sparc uses an idle function pointer in its architecture
specific code.  So we re-name sparc use of pm_idle to sparc_idle.

Signed-off-by: Len Brown <len.brown@intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>