Add defaults in SAMV7 configuration for all DAC settings

arch/arm/src/samv7/Kconfig

@@ -1668,9 +1668,28 @@ menu "DAC device driver configuration"
 
 config SAMV7_DAC_PRESCAL
 	int "DAC MCK prescaler"
+	default 7
+	range 0 15
 	---help---
 		Define PRESCALER (Peripheral Clock to DAC Clock Ratio)
 
+		 0 -> 2 periods of DAC Clock
+		 1 -> 3 periods of DAC Clock
+		 2 -> 4 periods of DAC Clock
+		 3 -> 5 periods of DAC Clock
+		 4 -> 6 periods of DAC Clock
+		 5 -> 7 periods of DAC Clock
+		 6 -> 8 periods of DAC Clock
+		 7 -> 9 periods of DAC Clock
+		 8 -> 10 periods of DAC Clock
+		 9 -> 11 periods of DAC Clock
+		10 -> 12 periods of DAC Clock
+		11 -> 13 periods of DAC Clock
+		12 -> 14 periods of DAC Clock
+		13 -> 15 periods of DAC Clock
+		14 -> 16 periods of DAC Clock
+		15 -> 17 periods of DAC Clock
+
 config SAMV7_DAC_TRIGGER
 	bool "DAC trigger mode"
 	default n
@@ -1681,16 +1700,21 @@ if SAMV7_DAC_TRIGGER
 
 config SAMV7_DAC_TRIGGER_FREQUENCY
 	int "DAC trigger frequency"
+	default 1000
 	---help---
 		Define DAC trigger frequency
 
 config SAMV7_DAC_TRIGGER_SELECT
 	int "DAC trigger source"
-	default 1
+	default 3
 	range 1 3
 	---help---
-		Define DAC trigger source (only support for TC0, TC1, TC2 output is
-		currently implemented)
+		Define DAC trigger source.  Snly support for TC0, TC1, TC2 output is
+		currently implemented:
+
+		1 -> TC0
+		2 -> TC1
+		3 -> TC2
 
 endif # SAMV7_DAC_TRIGGER
 endmenu # DAC device driver configuration