ARM: imx_v6_v7_defconfig: select CONFIG_ARM_CPUIDLE by default

Some i.MX platforms like i.MX7S/D uses generic ARM cpuidle
driver and psci method to support cpuidle feature, select
CONFIG_ARM_CPUIDLE by default for such platforms.
Signed-off-by: NAnson Huang <Anson.Huang@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -62,6 +62,7 @@ CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
 CONFIG_CPUFREQ_DT=y
 CONFIG_ARM_IMX6Q_CPUFREQ=y
 CONFIG_CPU_IDLE=y
+CONFIG_ARM_CPUIDLE=y
 CONFIG_VFP=y
 CONFIG_NEON=y
 CONFIG_BINFMT_MISC=m