Merge branch 'add-property-in-dwmac-stm32-documentation'

Christophe Roullier says:

====================
Add property in dwmac-stm32 documentation

Introduce property in dwmac-stm32 documentation

 - st,ext-phyclk: is present since 2020 in driver so need to explain
   it and avoid dtbs check issue : views/kernel/upstream/net-next/arch/arm/boot/dts/st/stm32mp157c-dk2.dtb:
ethernet@5800a000: Unevaluated properties are not allowed
('st,ext-phyclk' was unexpected)
   Furthermore this property will be use in upstream of MP13 dwmac glue. (next step)
====================

Link: https://lore.kernel.org/r/20240328185337.332703-1-christophe.roullier@foss.st.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>