ARM: dts: dra76-evm: Enable x2 PCIe lanes

DRA76 EVM has a 4-lane PCIe connector and DRA76 can support x2 lanes.
Enable both the PCIe lanes here.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>