Broken ACPI tables containing scopes that are larger than their outer shell

Broken ACPI tables containing scopes that are larger than their outer shell
are caught by our ACPI parser.  Unfortunately in such cases our reaction was
to start parsing AML somewhere outside our current scope.  The intention was
to clamp down the inner scope to the maximum of the outer one.  So, rectify it.

This issue has shown up in EDK2's QEMU SBSA target, where the SSDT table was
generated incorrectly.  Surprisingly neither Linux nor ACPICA's iASL noticed
that the table was broken.

ok kettenis@ millert@