Add predefined objects to AML interpreter

[IsaacWoods]

The firmware is allowed to assume that certain objects exist, that must be provided by the OSPM:

• [ ] \_GL - the global lock mutex
• [x] \_OS - the name of the OS (note that this shouldn't be set to your real OS's name, as many firmwares expect specific strings to work correctly)
• [x] \_OSI - Operating System Interface support. Allows the firmware to query whether the OS supports a feature or not.
• [x] \_REV - the revision of the ACPI spec that the AML interpreter supports. This should be set internally, and will probably have to be a lie until our supports gets better.