arm64: dts: ti: k3-am65*: Use generic gpio for node names

Use gpio@ naming for nodes following standard conventions of device
tree (section 2.2.2 Generic Names recommendation in [1]).

[1] https://github.com/devicetree-org/devicetree-specification/tree/v0.3



Suggested-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Acked-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20200903130015.21361-4-nm@ti.com