ARM: keystone: dts: fix dt bindings for PCIe

Currently PCIe DT bindings are broken. PCIe driver can't function
without having a SerDes driver that provide the phy configuration.
On K2E EVM, this causes problem since the EVM has Marvell SATA
controller present and with default values in the SerDes register,
it seems to pass the PCIe link check, but causes issues since
the configuration is not correct. The manifestation is that when
EVM is booted with NFS rootfs, the boot hangs. We shouldn't enable
PCIe on this EVM since to work, SerDes driver has to be present as
well. So by default, the PCIe DT binding should be disabled in SoC
specific DTS. It can be enabled in the board specific DTS when the
SerDes device driver is also present.

So fix the status of PCIe DT bindings in the SoC specific DTS to
"disabled". To enable PCIe, the status should be set to "ok" in
the EVM DTS file when SerDes driver support becomes available in
the upstream tree.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>