Add the standard extres pseudo devices to the IMX6 kernel config.

Some imx6 drivers are being converted to use features that weren't available
when they were first written (such as accessing shared device registers via
the syscon pseudo-device), so imx6 custom kernels that reference those
devices will now need this infrastructure in place.

sys/arm/conf/IMX6

@@ -117,6 +117,15 @@ options 	FDT			# Configure using FDT/DTB data
 makeoptions	MODULES_EXTRA="dtb/imx6 imx"
 device  	fdt_pinctrl		# FDT pinmux driver
 
+# EXT_RESOURCES pseudo devices
+options 	EXT_RESOURCES
+device		clk
+device		phy
+device		hwreset
+device		nvmem
+device		regulator
+device		syscon
+
 # SoC-specific devices
 device		ffec			# Freescale Fast Ethernet Controller
 device		fsliic			# Freescale i2c/iic