amd-xgbe: enable PLL_CTL for fixed PHY modes only

PLL control setting(RRC) is needed only in fixed PHY configuration to
fix the peer-peer issues. Without the PLL control setting, the link up
takes longer time in a fixed phy configuration.

Driver implements SW RRC for Autoneg On configuration, hence PLL control
setting (RRC) is not needed for AN On configuration, and can be skipped.

Also, PLL re-initialization is not needed for PHY Power Off and RRC
commands. Otherwise, they lead to mailbox errors. Added the changes
accordingly.

Fixes: daf182d3 ("net: amd-xgbe: Toggle PLL settings during rate change")
Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>