ipq806x: force 2nd pci slot into gen1 mode

ipq806x: force 2nd pci slot into gen1 mode

According to QSDK and OEM tarballs (checked c2600, r7500v2, r7800) 2nd pci slot (pci1, 2,4 GHz card)) on ap148 based boards should operate in gen1 mode.

In previous commit we've added the support for this option, so enable it in DT for affected devices.

QSDK ref:
https://source.codeaurora.org/quic/qsdk/oss/kernel/linux-msm/commit/?h=release/endive_preview_cc&id=f3b07fe309027c52fc163149500cedddd707c506

While at it move the phy transmit termination offset value into dtsi file as it's platform specific and disable the unequipped pcie2 in EA8500 DTS.

Signed-off-by: Pavel Kubelun <be.dissent@gmail.com>