permission(core): Modify protection level for SUBSCRIBE_TO_KEYGUARD

This is needed by NFC stack (which is a platform APK currently, but is
planned to become a mainline module in the future).

Bug: 227958253
Test: Compiles
Merged-In: Iaa22957057dad13df84cbbe7c7e92c47d4e79fa2

Change-Id: Iaa22957057dad13df84cbbe7c7e92c47d4e79fa2