PCI: mediatek-gen3: Rely on msleep() in mtk_pcie_en7581_power_up()

Since mtk_pcie_en7581_power_up() runs in non-atomic context, rely on
msleep() routine instead of mdelay().

Link: https://lore.kernel.org/r/20250108-pcie-en7581-fixes-v6-5-21ac939a3b9b@kernel.org


Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>