Change the global CFI flag to default to enabled.

This CL changes the ENABLE_CFI flag to default to enabled. Setting it
to false will override local settings to enable CFI.

Bug: 30227045
Bug: 22033465
Test: m -j40 works and device boots
Test: cfi is honored unless the global flag is set.
Change-Id: Ie3285c5eac60c8f6012c6b6c23be149a8787af0c

android/config.go

@@ -406,7 +406,11 @@ func (c *config) SanitizeDeviceArch() []string {
 }
 
 func (c *config) EnableCFI() bool {
-	return Bool(c.ProductVariables.EnableCFI)
+	if c.ProductVariables.EnableCFI == nil {
+		return true
+	} else {
+		return *c.ProductVariables.EnableCFI
+	}
 }
 
 func (c *config) Android64() bool {