FP4: Set PRODUCT_SET_DEBUGFS_RESTRICTIONS

Starting with Android R launched devices, debugfs cannot be mounted in
production builds. In order to avoid accidental debugfs dependencies
from creeping in during development with userdebug/eng builds, the
build flag PRODUCT_SET_DEBUGFS_RESTRICTIONS can be set by vendors to
enforce additional debugfs restrictions for userdebug/eng builds. The
same flag will be used to enable sepolicy neveallow statements to
prevent new permissions added for debugfs access.

Test: build, boot
Bug: 184381659
Change-Id: I45e6f20c886d467a215c9466f3a09965ff897d7e