[yocto] linux-firmware: add only rtl8192cufw.bin from rtlwifi

[Mårten Wikman]

Hello,

I want to install rtl8192cufw.bin from rtlwifi from linux-firmware but
if I add linux-firmware to IMAGE_INSTALL_append it will of course
install whole linux-firmware to my rootfs and bloats my rootfs image.

What is the correct way to install rtl8192cufw.bin automatically to my rootfs?