net/axgbe: toggle PLL settings during rate change

net/axgbe: toggle PLL settings during rate change

For each rate change command submission, the FW has to do a phy
power off sequence internally. For this to happen correctly, the
PLL re-initialization control setting has to be turned off before
sending mailbox commands and re-enabled once the command submission
is complete. Without the PLL control setting, the link up takes
longer time in a fixed phy configuration.

Signed-off-by: Selwin Sebastian <selwin.sebastian@amd.com>
Acked-by: Chandubabu Namburu <chandu@amd.com>