package/linux-firmware: install Xceive/Cresta xc4000 and xc5000c

Tweak the prompt, because Xceive is now part of Cresta, so the
new xc5000c-based devices might be branded under either name.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>