Platform/Sgi: add helper macros for acpi table generation

Add helper macros for generation of the MCFG, SSDT and IORT ACPI table.
The macro EFI_ACPI_SMMUv3_ID_TABLE_INIT simplifies the addition of the
SMMUv3 ID remapping table in the IORT table. The macro
EFI_ACPI_PCI_RC_ECAM_INIT describes the location of the PCI Express
configuration space in the MCFG ACPI table. The macro
EFI_ACPI_PCI_RC_INIT simplifies the addition of the root complex entry
in the SSDT ACPI table.

Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: Ic1b57cd1047d8940adc7909c33d57ffd728998f3