airoha: fix PERST deassert in PCIe driver

airoha: fix PERST deassert in PCIe driver

Due to hardware bugs, the PCIE Gen3 IP in Airoha AN7581 requires a
special reset procedure:
> MAC reset asserted thru the SCU block
> PERST asserted thru the SCU for the desired PCIE lane
> PHY initialization runs, clocks enabled
> MAC reset deasserted
> EQ config (if needed) written
> PERST deasserted

The existing code currently toggles PERST for all three PCIE
ports every time mtk_pcie_en7581_power_up is called, resulting
in PCIE link down issues.

This issue was discovered during porting of the 6.18 kernel to
AN7581. It is not entirely clear how the hardware seemed to
function under kernel 6.12 with similar driver code, it is
presumed that differences in assert/deassert times for PERST in
6.18 changed which exposed the bug.

Signed-off-by: Kenneth Kasilag <kenneth@kasilag.me>
Link: https://github.com/openwrt/openwrt/pull/21019
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>