ipq806x: disable CONFIG_CMDLINE_OVERRIDE and ASRock G10

ipq806x: disable CONFIG_CMDLINE_OVERRIDE and ASRock G10

After device support for ASRock G10 was added in [1], several
people reported broken ipq806x devices, with one or several of the
following symptoms:

  - Device does not boot
  - Sysupgrade does not work
  - Serial console is broken

The issues appears to be caused by the introduction of the symbol
CONFIG_CMDLINE_OVERRIDE=y in [1].

This patch disables the corresponding symbol again and marks the
ASRock as BROKEN, as it probably won't work properly without it.

Further references:

https://bugs.openwrt.org/index.php?do=details&task_id=3540
https://github.com/openwrt/openwrt/commit/98b86296e67dd2b467212fe1a577656e6d3725da#commitcomment-45455875

[1] 98b86296e67d ("ipq806x: add support for ASRock G10")

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>