realtek: switch Netgear NGE devices to rt-loader

realtek: switch Netgear NGE devices to rt-loader

The bootloader on these devices uses 0x81000000 as load address for the
compressed image. Since the kernel uses a load address 0x80100000, this
only leaves a space of 15 MiB for the uncompressed image. For larger
images, the compressed data starts to get overwritten, and at some point
the boot will fail:

    ## Booting image from partition ... 0
    ## Booting kernel from Legacy Image at 81000000 ...
       Version:      9.9.9.9
       Created:      2025-08-07  14:56:09 UTC
       Data Size:    6756645 Bytes = 6.4 MB
       Checksum ... OK
       Uncompressing ... LZMA: uncompress or overwrite error 1 - must RESET board to recover

Currently, initramfs images with default config are already over the
limit. And while they still happen to work regardless, adding additional
packages easily pushes the size so much that the boot fails.

Fix this by switching to rt-loader (which relocates the data to the
upper end of the RAM before decompression). The switch includes regular
kernel images to avoid this becoming an issue again in the future.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>
Link: https://github.com/openwrt/openwrt/pull/19734
Signed-off-by: Robert Marko <robimarko@gmail.com>