lantiq: xrx200_legacy: disable unused phy drivers

lantiq: xrx200_legacy: disable unused phy drivers

Subtarget xrx200_legacy supports only a few devices. They all use
the integrated Lantiq GSWIP switch and lantiq xway PHYs. The atheros
and icplus PHYs can be safely disabled.

Switches used by individual devices are listed below.

Device				Switch			PHY
Alpha ASL56026			Lantiq GSWIP		int. switch
Arcadyan VG3503J		Lantiq GSWIP		int. switch
Netgear DM200			Lantiq GSWIP		int. switch
TP-LINK TD-W8970		Lantiq GSWIP		Lantiq PEF7071V
TP-Link TD-W8980		Lantiq GSWIP		Lantiq PEF7071V

Reduces uncompressed kernel size by 16 kB.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Link: https://github.com/openwrt/openwrt/pull/17581
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 517b9c1cdcd357fd84c7f27bd2886f235f3ec946)