Implemented reading from RTC Century counter in x86_64 arch, if available
Created by: CWood1
The ACPI code now saves the FADT in a globally accessible mutex, with infrastructure in place to add additional tables to the mutex if necessary.
The x86_64 device initialization has been split into "core" devices necessary for initialization, and "non-core" devices not necessary to bring the kernel up, which are initialized, respectively, before and after ACPI.
The RTC read function now checks for the presence of the FADT, and, if present, uses the century register indicated in the table. If not present, it defaults to assuming the 21st century as before.