Add component-override to sysconfig

The <component-override> tag in sys config allows an OEM to configure
the enabled state of package components.

Eg.
<!-- Disable com.foo.bar.MyActivity -->
<component-override package="com.foo.bar">
    <component class=".MyActivity" enabled="false">
</component-override>

The value in the sys config file overrides the value defined within
the package manifest.

Bug: 135048762
Test: adb shell pm resolve-activity
com.android.settings/com.android.settings.RegulatoryInfoDisplayActivity

Change-Id: I71de31601bb175d4be1cc5996142ef93ca279fc1