ARM: imx6: fix static declaration in include/soc/imx/cpuidle.h

If both CONFIG_CPU_IDLE or CONFIG_SOC_IMX6Q are not set
then the imx6q_cpuidle_fec_irqs_used() and other functions
should be marked static inline to avoid the following
warnings whilst building drivers/net/ethernet/freescale:

include/soc/imx/cpuidle.h:21:6: warning: symbol 'imx6q_cpuidle_fec_irqs_used' was not declared. Should it be static?
include/soc/imx/cpuidle.h:22:6: warning: symbol 'imx6q_cpuidle_fec_irqs_unused' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>