ARM: defconfig: imx_v6_v7: build in REGULATOR_FIXED_VOLTAGE

Some devices on some imx boards are supplied by fixed voltage, so
build REGULATOR_FIXED_VOLTAGE support in.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -124,6 +124,7 @@ CONFIG_WATCHDOG=y
 CONFIG_IMX2_WDT=y
 CONFIG_MFD_MC13XXX=y
 CONFIG_REGULATOR=y
+CONFIG_REGULATOR_FIXED_VOLTAGE=y
 CONFIG_REGULATOR_MC13892=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y