defconfig: apq8084: add atheros ethernet

Add defconfig flag for compiling atheros ethernet driver.
The driver is required for the atheros ethernet chip
used on apq8084 devices.

Change-Id: I664b22ea5f587b202270ba3e6123a3981e6a5b75
Signed-off-by: Ilia Lin <ilialin@codeaurora.org>