doc: phy: Document typical order of API calls

Document the typical order of API calls to used by new drivers and
controllers. Many existing controllers follow this order, but some do
not. This is especially true for controllers designed to work with one
particular PHY driver, which may not need a call to (for example)
phy_init.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20221018175841.1906611-1-sean.anderson@seco.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>