imx: introduce CONFIG_GPT_TIMER

Introduce a new config symbol to select the i.MX
General Purpose Timer (GPT).

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/arch/arm/mach-imx/mx6/Kconfig b/arch/arm/mach-imx/mx6/Kconfig
index 2552a50..8944432 100644
--- a/arch/arm/mach-imx/mx6/Kconfig
+++ b/arch/arm/mach-imx/mx6/Kconfig
@@ -9,6 +9,7 @@
 
 config MX6
 	select ARM_ERRATA_743622 if !MX6UL && !MX6ULL
+	select GPT_TIMER
 	bool
 	default y
 	imply CMD_FUSE