ramips: disable build TP-Link EAP235-Wall

ramips: disable build TP-Link EAP235-Wall

After investigating the EAP235-Wall u-boot GPL code, it was found that
the u-boot of this device directly loads the kernel from the SPI NOR
Flash direct access address. However, due to hardware limitation, MT7621
can only remap the first 4MiB Flash. Excluding some partitions before
the kernel, this device can only boot kernels smaller than 0x360000.
This means that unless you install a modified bootloader, the mainline
OpenWrt will no longer work on this model.

Closes: https://github.com/openwrt/openwrt/issues/20500
Signed-off-by: Shiji Yang <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20509
Signed-off-by: Robert Marko <[email protected]>