Add getHal and getHals to VendorManifest.

Part of the effort to hide implementation details in libvintf.

Bug: 34620633

Test: libvintf_test
Change-Id: I673fa29be833f023ffe29ece0b3295cec2203e19
diff --git a/parse_string.cpp b/parse_string.cpp
index d2584ec..b0c8657 100644
--- a/parse_string.cpp
+++ b/parse_string.cpp
@@ -223,8 +223,7 @@
 std::string dump(const VendorManifest &vm) {
     std::ostringstream oss;
     bool first = true;
-    for (const auto &pair : vm.hals) {
-        const auto &hal = pair.second;
+    for (const auto &hal : vm.getHals()) {
         if (!first) {
             oss << ":";
         }