marvell: comphy: update rx_training procedure

1) Relay only on rx training, remove parts responsible for tx training
(trx training).
2) Add extra steps e.g. preconfigure FFE before starting training.
3) Remove some unnecessary steps like RRBS31 loopback setting which
shouldn't be relevant for tx_training.

Change-Id: Ib1e8567714f9ce33578186a262c339aa4b1c51f2
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
2 files changed