Avoid calling DepIsInSameApex when excluded from apex contents

While debugging an issue with some work I was doing on boot image
modules I noticed that markPlatformAvailability() is calling
DepIsInSameApex() even when the dependency tag indicates that it is
excluded from the apex contents.

Test: m droid
Change-Id: Iac49049546a886f7a3a0d9640ffd31ce24c61364
diff --git a/apex/apex.go b/apex/apex.go
index efd1736..35b4ba8 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -970,6 +970,10 @@
 	// If any of the dep is not available to platform, this module is also considered as being
 	// not available to platform even if it has "//apex_available:platform"
 	mctx.VisitDirectDeps(func(child android.Module) {
+		depTag := mctx.OtherModuleDependencyTag(child)
+		if _, ok := depTag.(android.ExcludeFromApexContentsTag); ok {
+			return
+		}
 		if !am.DepIsInSameApex(mctx, child) {
 			// if the dependency crosses apex boundary, don't consider it
 			return