PCI: mediatek-gen3: Add comment about initialization order in mtk_pcie_en7581_power_up()

Add a comment in mtk_pcie_en7581_power_up() to clarify, unlike the other
MediaTek Gen3 controllers, the Airoha EN7581 requires PHY initialization
and power-on before PHY reset deassert.

Link: https://lore.kernel.org/r/20250108-pcie-en7581-fixes-v6-3-21ac939a3b9b@kernel.org
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

Author: LorenzoBianconi

drivers/pci/controller/pcie-mediatek-gen3.c

@@ -925,6 +925,10 @@ static int mtk_pcie_en7581_power_up(struct mtk_gen3_pcie *pcie)
 	/* Wait for the time needed to complete the reset lines assert. */
 	mdelay(PCIE_EN7581_RESET_TIME_MS);
 
+	/*
+	 * Unlike the other MediaTek Gen3 controllers, the Airoha EN7581
+	 * requires PHY initialization and power-on before PHY reset deassert.
+	 */
 	err = phy_init(pcie->phy);
 	if (err) {
 		dev_err(dev, "failed to initialize PHY\n");