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/Kconfig b/arch/arm/mach-imx/Kconfig
index 6538191..3aec89d 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -10,6 +10,9 @@
 config SYSCOUNTER_TIMER
 	bool
 
+config GPT_TIMER
+	bool
+
 config IMX_RDC
 	bool "i.MX Resource domain controller driver"
 	depends on ARCH_MX6 || ARCH_MX7