Add fs_config entry for *.rc files.

Android init will refuse to read files that are world writable. Since
adb push makes files world writable by default, this means that adb
pushed rc files cannot be read by init. Fix it by adding an fs_config
entry for *.rc that sets their permissions to 644 root:root.

Bug: 343370899
Change-Id: If9c4dd4796caae6d177d9fdeef880949e5639648