dumpstate: mount debugfs in non-user builds

This change will help non-user builds with keeping debugfs
disabled during run time. Instead, it will be mounted by dumpstate
for bug report generation and unmounted after. Access to debugfs
will be restricted to dumpstate HAL.

Test: adb shell am bug-report
Bug: 176936478
Change-Id: Icbe318399f50ca467f5ab9c414ddae5098826301