net: ethernet: ti: am65-debugfs: Fix kernel crash if CONFIG_DEBUG_FS is not set in .config

Kernel boot crashes if CONFIG_DEBUG_FS is not set in .config. The cpsw-nuss
driver does not handle this case.

Fix the issue by implementing empty debugfs APIs

Signed-off-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>