DynamicTablesPkg: AML Field list parser

The AML language allows defining field lists in a Definition
Block. Although Dynamic AML does not provide interfaces to
modify Field Lists; an AML template code may contain Field
lists and the AML parser must be capable of parsing and
representing the Field lists in the AML tree.

The AML parser creates an Object node that represents the
'Field Node'. The AML Field list parser creates an object
node for each field element parsed in the AML byte stream,
and adds them to the variable list of arguments of the
'Field Node'.

Nodes that can have a field list are referred as 'Field
nodes'. They have the AML_HAS_FIELD_LIST attribute set in
the AML encoding.

According to the ACPI 6.3 specification, s20.2.5.2 "Named
Objects Encoding", field elements can be:
 - NamedField           := NameSeg PkgLength;
 - ReservedField        := 0x00 PkgLength;
 - AccessField          := 0x01 AccessType AccessAttrib;
 - ConnectField         := <0x02 NameString> | <0x02 BufferData>;
 - ExtendedAccessField  := 0x03 AccessType ExtendedAccessAttrib
                             AccessLength.

A small set of opcodes describes the field elements. They are
referred as field opcodes. An AML_BYTE_ENCODING table has been
created for field OpCodes.
Field elements:
 - don't have a SubOpCode;
 - have at most 3 fixed arguments (as opposed to 6 for standard
     AML objects);
 - don't have a variable list of arguments;
 - only the NamedField field element is part of the AML namespace.

ConnectField's BufferData is a buffer node containing a single
resource data element.
NamedField field elements do not have an AML OpCode. NameSeg
starts with a Char type and can thus be differentiated from the
Opcodes for other fields.

A pseudo OpCode has been created to simplify the parser.

Following is a representation of a field node in an AML tree:
(FieldNode)
    \
     |- [0][1][3]                      # Fixed Arguments
     |- {(FldEl0)->(FldEl1)->...)}     # Variable Arguments

Where FldEl[n] is one of NamedField, ReservedField, AccessField,
ConnectField, ExtendedAccessField.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>

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