This splits setting the power mode of the controller / phy in two
functions. It's done in preparation of setting up the phy based on the
pixelclock.

No functional changes intended.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222174220.55249-23-knaerzche@gmail.com