arm64: dts: ti: j7200-main: Add *max-virtual-functions* for pcie-ep DT node

J7200 has 4 virtual functions for the first four physical function.
Add *max-virtual-functions* in pcie-ep DT node to represent the same.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20210915055358.19997-6-kishon@ti.com