watchdog: atmel_sam: only build for SAME70

With recent changes we now have both SAME70 and SAM3X under
SOC_FAMILY_SAM so we need to limit the watchdog driver only to SAME70 as
it only builds there right now.

Change-Id: I4a7c90247ad22532b2384ca536cfb0cbd65186f9
Signed-off-by: Kumar Gala <[email protected]>

Author: galak

drivers/watchdog/Kconfig.sam

@@ -7,7 +7,7 @@
 
 menuconfig WDT_SAM
 	bool "Atmel SAM MCU Family Watchdog (WDT) Driver"
-	depends on SOC_FAMILY_SAM
+	depends on SOC_SERIES_SAME70
 	default y
 	help
 	  Enable WDT driver for Atmel SAM MCUs.