After converting to multiplatform the old IXP4xx defconfig
doesn't even activate the ethernet driver anymore, we need
to refresh this thoroughly.

- Drop options that ARCH_MULTI_V5 selects for us.
- Some options moved around because of multiplatform and
  because generic Kconfig movements.
- Drop all MACH_* that do not exist anymore.
- Compress the kernel and initramfs with XZ as the memory
  is often limited for these machines.
- Make sure IXP4XX_QMGR and IXP4XX_NPE is selected.
- Make sure the MTD_PHYSMAP_IXP4XX is selected and not
  the old MTD_IXP4XX (will be deleted).
- Activate CRYPTO_DEV_IXP4XX
- Add some very basic default drivers such as AT24 EEPROMs
  used in many routers.
- Add some kernel configs needed to bring up OpenWrt
  which is the only userspace for these devices:
  CGROUPS, DEVTMPFS, INOTIFY_USER, SIGNALFD, TIMERFD,
  EPOLL, OVERLAY_FS and SQUASHFS.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Krzysztof Halasa <khalasa@piap.pl>
Cc: Imre Kaloz <kaloz@openwrt.org>
Link: https://lore.kernel.org/r/20220407204502.2470560-1-linus.walleij@linaro.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>