timer: imx-gpt: Add timer support for i.MX SoCs family

This timer driver uses GPT Timer (General Purpose Timer) available on
a lot of i.MX SoCs family. This driver deals with both 24Mhz oscillator
as well as peripheral clock.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
[Giulio: added the driver's stub and handled peripheral clock prescaler
setting making driver to work correctly]
Signed-off-by: Jesse Taube <mr.bossman075@gmail.com>
[Jesse: added init, setting prescaler for 24Mhz support and enabling
timer]
diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index 80743a2..ee81dfa 100644
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -227,4 +227,11 @@
 	  Select this to enable support for Microchip 64-bit periodic
 	  interval timer.
 
+config IMX_GPT_TIMER
+	bool "NXP i.MX GPT timer support"
+	depends on TIMER
+	help
+	  Select this to enable support for the timer found on
+	  NXP i.MX devices.
+
 endmenu