PCI: mediatek-gen3: Avoid PCIe resetting via PERST# for Airoha EN7581 SoC

PCI: mediatek-gen3: Avoid PCIe resetting via PERST# for Airoha EN7581 SoC

Airoha EN7581 has a hw bug asserting/releasing PERST# signal causing
occasional PCIe link down issues. In order to overcome the problem,
PERST# signal is not asserted/released during device probe or
suspend/resume phase and the PCIe block is reset using
en7523_reset_assert() and en7581_pci_enable().

Introduce flags field in the mtk_gen3_pcie_pdata struct in order to
specify per-SoC capabilities.

Link: https://lore.kernel.org/r/20250109-pcie-en7581-rst-fix-v4-1-4a45c89fb143@kernel.org
Tested-by: Hui Ma <hui.ma@airoha.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>