net: mvpp2: Add ksettings cross phy interface configuration support

commit 80b1460c342bcb6c6ad9fa3c7fc8330ae9fc5d49 from
git@git.assembla.com:cavium/WindRiver.linux.git

Proposal:
speed change 10G/5G/2.5G/1G over ethtool ksettings

Current situation:
- Init with speed=10G, autoneg=ON and
 advertising for 10/100/1000M(baseT)/10G(baseKR/SR/LR)
- Speed set to 1G failed

Code findings:
Port speed change mvpp2_mac_config() called from phylink
applied upon the given INTERFACE-TYPE but not upon speed
=> The required FIX is in the phylink:
=> phylink_ethtool_ksettings_set() should modify the
   PHY_INTERFACE_MODE_xx (10GKR/5KR/2500BASEX/2500BASEX/1000BASEX)
   according to the required kset.speed if PHYDEV doesn't exist

SOLUTIONs:
mvpp2_get_interface_by_speed() introduced

Change-Id: I906e3c695c4ebcd48072aaf284282997b228ea9d
Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/56077
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Yan Markman <ymarkman@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/56128
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>