drm/mediatek: dp: Enable event interrupt only when bridge attached

It is useless and error-prone to enable the DisplayPort event interrupt
before finishing to probe and install the driver, as the DP training
cannot happen before the entire pipeline is correctly set up, as the
interrupt handler also requires the full hardware to be initialized by
mtk_dp_bridge_attach().

Anyway, depending in which state the controller is left from the
bootloader, this may cause an interrupt storm and consequently hang
the kernel during boot, so, avoid enabling the interrupt until we
reach a clean state by adding the IRQ_NOAUTOEN flag before requesting
it at probe time and manage the enablement of the ISR in the .attach()
and .detach() handlers for the DP bridge.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230725073234.55892-7-angelogioacchino.delregno@collabora.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>