realtek: image: add rt-loader-no-uimage recipe

realtek: image: add rt-loader-no-uimage recipe

Add a new recipe 'rt-loader-no-uimage' that passes the kernel load
address to rt-loader, causing it to use that instead of it's initial run
address.

The usual behavior is fine for uImages where the load address is
predefined in the header, U-boot loads the image to that address and
then runs it, rt-loader just takes over that address. For non-uImage
instead, the address is tightly coupled to where the image has been
transferred during serial or TFTP upload. This may not be possible on
several devices. Passing a separate kernel load address to rt-loader
decouples that and avoids taking the pain to change the load address of
the kernel itself.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21248
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>