data-kernel: EMAC: Fixed ethool speed issue.

Don't modify emac supported capabilities during
early ethernet boot up. Only update advertise values
otherwise speed can't be changed using ethtool.

Change-Id: I06a2d5cd93fec14cd107d7c4c39e704163369e80
CRs-Fixed: 2416416
Signed-off-by: Sunil Paidimarri <hisunil@codeaurora.org>