ARM: introduce common set_auxcr/get_auxcr functions

Move the private set_auxcr/get_auxcr functions from
drivers/cpuidle/cpuidle-calxeda.c so they can be used across platforms.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>