Add support for Eagle with separate lm-head and embed_tokens layers (#28549)

Signed-off-by: Eldar Kurtic <8884008+eldarkurtic@users.noreply.github.com>

tests/v1/spec_decode/test_mtp.py

@@ -67,6 +67,10 @@ def test_mtp_load_model_unified(mock_get_model, mock_get_layers, mock_get_pp_gro
     mock_model = mock.MagicMock()
     mock_model.model.embed_tokens.weight.shape = (131072, 4096)
     mock_get_model.return_value = mock_model
+    # MTP does not have its own embed_tokens or lm_head
+    # so it should share them with the target model
+    mock_model.has_own_embed_tokens = False
+    mock_model.has_own_lm_head = False
 
     target_attn_layers = {"target_attn_1": mock.MagicMock()}
     all_attn_layers = {**target_attn_layers, "draft_attn_1": mock.MagicMock()}