AcpiDump/Linux version: Restructure code and some cleanup.

Add a couple new subroutines to clarify the code, cleanup some
loops, error messages, and constants. Chao Guan.
AcpiDump: Allow FADT/MADT as valid signatures, cleanup.

To be friendly, allow FADT and MADT as synonyms for FACP and APIC.
Cleanup some error messages.