firmware: Be clearer about where load errors originate

[thj]

Summary

When we load firmware we first try and find a kernel module and then try
to load a file from the firmware path (/boot/firmware by default).

When the module fails to load we currently print a failure, but we don't
print a success message if we manage to load from a file.

With the move of wifi firmware from a kernel module to binary files many
users are seeing firmware load errors when the module isn't there and
these errors are being added to bug reports.

To avoid user confusion only print firmware load failures if we are
verbose, or if no firmware can be loaded.

Adjust some messages to make it clearer which firmware has failed to load.

[thj]

Meant to add:

I'm happy to have a discussion about what the right thing to do is, this is just a first pass at trying to make loading less likely to cause confusion.

[bz]

sys/kern/subr_firmware.c

356

Please do not remove that. I believe LinuxKPI sets it as otherwise (on boot-v) we get up to three reports about the same file not loaded

sys/compat/linuxkpi/common/src/linux_firmware.c:        flags = FIRMWARE_GET_NOWARN;