firmware loader: introduce module parameter to customize(v4) fw search path

firmware loader: introduce module parameter to customize(v4) fw search path

This patch introduces one module parameter of 'path' in firmware_class
to support customizing firmware image search path, so that people can
use its own firmware path if the default built-in paths can't meet their
demand[1], and the typical usage is passing the below from kernel command
parameter when 'firmware_class' is built in kernel:

	firmware_class.path=$CUSTOMIZED_PATH

[1], https://lkml.org/lkml/2012/10/11/337

Cc: Linus Torvalds <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>