AA: ar71xx: disable PHY_SWAP and PHY_ADDR_SWAP bits on TL-WR703N/MR3020/MR3040/MR11U boards

Backport of r35037.

The PHY_SWAP and PHY_ADDR_SWAP bits are initialized
differently by different versions of the bootloader.
This leads to broken ethernet connection with OpenWrt
on some boards.

Turn both SWAP bits OFF on these boards to make it
consistent regardless of the bootloader used.

Based on a patch by Michel Stempin <michel.stempin@wanadoo.fr>.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/branches/attitude_adjustment@35038 3c298f89-4303-0410-b956-a3cf2f4a3e73