Driver core: Reduce the level of request_firmware() messages

The messages from _request_firmware() informing that firmware is
being requested or built-in firmware is going to be used are printed
at KERN_INFO, which produces lots of noise on systems with huge
numbers of AMD CPUs.  Reduce the level of these messages to
KERN_DEBUG to get rid of that noise.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>