DynamicTablesPkg: Add AmlAttachNode()

DynamicTablesPkg: Add AmlAttachNode()

This function allows to add a node as the last node of a parent node
in an AML tree. For instance,
ASL code corresponding to NewNode:
  Name (_UID, 0)

ASL code corresponding to ParentNode:
  Device (PCI0) {
    Name(_HID, EISAID("PNP0A08"))
  }

"AmlAttachNode (ParentNode, NewNode)" will result in:
ASL code:
  Device (PCI0) {
    Name(_HID, EISAID("PNP0A08"))
    Name (_UID, 0)
  }

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