watchdog: imx2_wdt: convert to use regmap API.

This watchdog driver will be working on IMX2+, Vybrid, LS1, LS2+
platforms, and will be in different endianness mode in those SoCs:

SoCs         CPU endian mode      WDT endian mode
------------------------------------------------
IMX2+            LE                    LE
Vybird           LE                    LE
LS1              LE                    BE
LS2              LE                    LE

Other possible SoCs:
SoCs         CPU endian mode      WDT endian mode
------------------------------------------------
Soc1             BE                    BE
Soc2             BE                    LE

And also the watchdog's registers will be 32-bits for some versions,
and though it is 16-bits in IMX2+, Vybird and LS+.

Using the regmap APIs, could be more easy to support different
endianness and also more easy to support 32-bits version...

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 2b4c1fc..65ef91e 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -378,6 +378,7 @@
 config IMX2_WDT
 	tristate "IMX2+ Watchdog"
 	depends on ARCH_MXC
+	select REGMAP_MMIO
 	help
 	  This is the driver for the hardware watchdog
 	  on the Freescale IMX2 and later processors.