Platform/ARM/Sgi: Refactor ACPI tables for SGI platforms

ACPI tables Dbg2.aslc, Fadt.aslc, Gtdt.aslc, Iort.aslc, Mcfg.aslc,
Spcr.aslc and Ssdt.asl are common for SGI platforms. To reduce
duplication of ACPI tables when new platforms are added these tables
are moved to the AcpiTables folder. Only platform specific tables
Dsdt.asl and Madt.aslc remain in the platform specific folder. Also
the AcpiTables.inf file is renamed as Sgi575AcpiTables.inf and moved to
AcpiTables folder.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>