packages/apps/Car/SystemUpdater: Set LOCAL_SDK_VERSION where possible.

This change sets LOCAL_SDK_VERSION for all packages where
this is possible without breaking the build, and
LOCAL_PRIVATE_PLATFORM_APIS := true otherwise.

Setting one of these two will be made required soon, and this
is a change in preparation for that. Not setting LOCAL_SDK_VERSION
makes the app implicitly depend on the bootclasspath, which is
often not required. This change effectively makes depending on
private apis opt-in rather than opt-out.

Test: make relevant packages
Bug: 73535841
Change-Id: Ibde47d6c3f5dccf01f55fb591e9942d2aa9542f1
diff --git a/Android.mk b/Android.mk
index dea6312..c305684 100644
--- a/Android.mk
+++ b/Android.mk
@@ -24,6 +24,7 @@
 LOCAL_CERTIFICATE := platform
 
 LOCAL_PACKAGE_NAME := SystemUpdater
+LOCAL_PRIVATE_PLATFORM_APIS := true
 
 LOCAL_DEX_PREOPT := false