ARM: imx: add gpt_3m clk for i.mx6qdl

Add gpt_3m clock for i.mx6qdl, as gpt can source clock
from OSC, some i.MX6 series SOCs has fixed divider of
8 for gpt clock, so here add a fix clk of gpt_3m.

i.MX6Q TO1.0 has no gpt_3m option, so force it to be
from ipg_per.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

include/dt-bindings/clock/imx6qdl-clock.h

@@ -247,6 +247,7 @@
 #define IMX6QDL_PLL5_BYPASS			234
 #define IMX6QDL_PLL6_BYPASS			235
 #define IMX6QDL_PLL7_BYPASS			236
-#define IMX6QDL_CLK_END				237
+#define IMX6QDL_CLK_GPT_3M			237
+#define IMX6QDL_CLK_END				238
 
 #endif /* __DT_BINDINGS_CLOCK_IMX6QDL_H */