net: macb: Clean up the .clk_init setting in the macb_config instances

net: macb: Clean up the .clk_init setting in the macb_config instances

All instances of macb_config currently have .clk_init set, but most of
them use macb_clk_init(). In fact, there is no need to duplicate this
across all macb_config instances. Introduce a new macb_clk_init()
function that executes the specific .clk_init if it is set; otherwise,
it runs the default clock initialization function.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Link: https://patch.msgid.link/20260310-macb-cleanup-v1-1-928c1a91a7dc@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>