Bluetooth: Add debugfs support to btmrvl driver

/debug/btmrvl/config/
/debug/btmrvl/status/

See Documentation/btmrvl.txt for details.

This patch incorporates a lot of comments given by
Nicolas Pitre <nico@marvell.com>. Many thanks to Nicolas Pitre.

Signed-off-by: Rahul Tank <rahult@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>