Fix arm platform matching

The normalization was being inconsistently applied causing a
failure to match some platforms in manifest lists.
Fix the matcher and normalization to be more consistent and
add changes to parser to prevent the defaulted variants from being
set in the platform structure.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

platforms/database.go

@@ -89,18 +89,21 @@ func normalizeArch(arch, variant string) (string, string) {
 	case "x86_64", "x86-64":
 		arch = "amd64"
 		variant = ""
-	case "aarch64":
+	case "aarch64", "arm64":
 		arch = "arm64"
-		variant = "" // v8 is implied
+		switch variant {
+		case "", "8":
+			variant = "v8"
+		}
 	case "armhf":
 		arch = "arm"
-		variant = ""
+		variant = "v7"
 	case "armel":
 		arch = "arm"
 		variant = "v6"
 	case "arm":
 		switch variant {
-		case "v7", "7":
+		case "", "7":
 			variant = "v7"
 		case "5", "6", "8":
 			variant = "v" + variant
@@ -109,3 +112,15 @@ func normalizeArch(arch, variant string) (string, string) {
 
 	return arch, variant
 }
+
+// defaultVariant detects default variants on normalized arch/variant
+func defaultVariant(arch, variant string) bool {
+	switch arch {
+	case "arm64":
+		return variant == "v8"
+	case "arm":
+		return variant == "v7"
+	default:
+		return true
+	}
+}