phy: ti: gmii-sel: move phy init in separate function

Move phy initialization in separate function to improve code readability
and simplify future changes.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Link: https://lore.kernel.org/r/20200828201943.29155-2-grygorii.strashko@ti.com


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