meta-ked-imx: u-boot-ktn: osm-s-mx93.env: add rw to bootargs_base

A fitimage for iMX93 SOM, produces following errors if booted with default environment:

udevd[115]: bind failed: Read-only file system
udevd[115]: error binding udev control socket

As a result, some kernel modules are not loaded during boot: dwmac_imx, at24, ...

To temporary work around this problem add a "rw" argument to kernel cmdline.

Probably, more elegant solution exists, but more time is needed to dig into this issue further.