lantiq: xrx200: disable unused switch and phy

lantiq: xrx200: disable unused switch and phy

xrx200 has a 6 port built-in switch with 2 integrated PHY. None of the
xrx200 router uses external switch. Most boards use integrated or Lantiq
(Intel) PEF7071 PHY. Only some FritzBox routers use AT803X PHY and
VGV7510KW22 use ICPLUS PHY. Other unused PHY drivers may be removed.

This patch enables these symbols only on xway and xway_legacy subtargets:
 - CONFIG_PSB6970_PHY (Driver for PHY in PSB6970 - 7 port FE Switch)
 - CONFIG_RTL8366RB_PHY (Driver for PHY in RTL8366 - 6 port GE Switch)
 - CONFIG_RTL8366_SMI (Driver for RTL8366 - 6 port GE Switch)

Reduces image size by 7.3kB.

Continuation of 58a6f06978f8 (PR: #2983)

Signed-off-by: Aleksander Jan Bajkowski <A.Bajkowski@stud.elka.pw.edu.pl>
[fix sorting in config files, small fix in commit message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>