board: at91sam9261ek: Update to support DT and DM

Add the dts files to support deivce tree, update the configuration
files to support the device tree and driver model. The peripheral
clock and pins configuration are handled by the clock and the pinctrl
drivers respectively.

Enable the early debug UART to debug problems when an ICE or other
debug mechanism is not available.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index 033c1ef..23ddc62 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -36,6 +36,7 @@
 config TARGET_AT91SAM9261EK
 	bool "Atmel at91sam9261 reference board"
 	select CPU_ARM926EJS
+	select BOARD_EARLY_INIT_F
 
 config TARGET_PM9261
 	bool "Ronetix pm9261 board"