UBUNTU: d-i: initrd needs qcom_emac on amberwing platform.

UBUNTU: d-i: initrd needs qcom_emac on amberwing platform.

Qualcom Centriq 2400 systems have an onboard two port nic that
uses qcom_emac driver. Add it to d-i's initrd so that these nics can
be used to d-i install the system. Tested on Qualcomm Centriq 2400
system at Canonical.

BugLink: http://bugs.launchpad.net/bugs/1677297
Signed-off-by: Manoj Iyer <manoj.iyer@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>