bootstat: lock down *_boot_reason_prop

Add series of neverallow rules to restrict components from reading or
writing bootloader_boot_reason_prop, system_boot_reason_prop and
last_boot_reason_prop to trusted set of domains.

The policy is that bootloader_boot_reason_prop (ro.boot.bootreason)
has a compliance issue due to the sheer momentum of near unparseable
content as filed by the wide variety (8000 different devices at last
count) bootloaders and is only to be accessible to a series of
responsible system components.  It can be inaccurate as it provides
no means to evaluate a shutdown, likely reporting "cold" (from
initial power up) or the more generic "reboot".

The last_boot_reason_prop (persist.sys.boot.reason) contains
inaccurate information as it is only valid after a controlled reboot
or shutdown.  The value can linger around after less controlled
scenarios.  Since the information could be false, we do not want to
support it as an open API, so we again block access to only
responsible components.

The system_boot_reason_prop (sys.boot.reason) is a canonical boot
reason that takes into account parsing bootloader_boot_reason_prop,
boot_loader_boot_reason_prop and other system and HAL generated hints
to determine a parseable and most accurate reason for the last time
the system was rebooted.

For now the policy for system_boot_reason_prop is to audit users of
the API, and on a need to know basis via device additions to the
selinux rules.  If vendors need their components to access the boot
reason, they need to comply first with CTS tests and spirit with
regards to controlled reboot messaging and in turn read the
system_boot_reason_prop for the canonical information.  It will
contain validated content derived from bootloader_boot_reason_prop
in the scenarios that count.

The controlled reboot APIs include:
- android_reboot(ANDROID_RB_<TYPE>, int flag, const char* reason)
- PowerManagerService.lowLevelShutdown(String reason);
- PowerManagerService.lowLevelReboot(String reason);
- ShutdownThread.shutdown(context, String reason, boolean confirm);
- ShutdownThread.reboot(context, String reason, boolean confirm);
- PowerManager.shutdown(boolean confirm, String reason, boolean wait);
- PowerManager.reboot(String reason);

Any others (including the direct linux reboot syscall) create
problems for generating an accurate canonical boot reason.

Test: compile
Bug: 63736262
Bug: 65686279
Change-Id: I2e5e55bbea1c383c06472eb2989237cfeb852030