net: axienet: Fix kernel doc warnings

net: axienet: Fix kernel doc warnings

Add description of mdio enable, mdio disable and mdio wait functions.
Add description of skb pointer in axidma_bd data structure.
Remove 'phy_node' description in axienet local data structure since
it is not a valid struct member.
Correct description of struct axienet_option.

Fix below kernel-doc warnings in drivers/net/ethernet/xilinx/:
1) xilinx_axienet_mdio.c:1: warning: no structured comments found
2) xilinx_axienet.h:379: warning: Function parameter or struct member
'skb' not described in 'axidma_bd'
3) xilinx_axienet.h:538: warning: Excess struct member 'phy_node'
description in 'axienet_local'
4) xilinx_axienet.h:1002: warning: expecting prototype for struct
axiethernet_option. Prototype was for struct axienet_option instead

Signed-off-by: Suraj Gupta <suraj.gupta2@amd.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://lore.kernel.org/r/20240328110713.12885-1-suraj.gupta2@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>