ARM: imx6q: export cpuidle functions needed by fec driver

Export cpuidle functions needed by fec driver to fix the issue below
seen with fec module build.

ERROR: "imx6q_cpuidle_fec_irqs_unused" [drivers/net/ethernet/freescale/fec.ko] undefined!
ERROR: "imx6q_cpuidle_fec_irqs_used" [drivers/net/ethernet/freescale/fec.ko] undefined!

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>