MdePkg: Add AML FieldList OpCode definitions

MdePkg: Add AML FieldList OpCode definitions

The ACPI specification, version 6.3, January 2019,
defines the Named Objects Encoding for FieldElements
in section '20.2.5.2 Named Objects Encoding'.
FieldElements can be one of the following:
NamedField | ReservedField | AccessField |
ExtendedAccessField | ConnectField

Some of these keywords are starting with an opcode,
allowing to identify their type.
E.g.: ReservedField := 0x00 PkgLength

This patch adds these FieldElement opcodes definitions to
the list of AML Opcode definitions.

Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>