Bluetooth: btmrvl: add DT-bindings for gpio-gap

This can be used to have GPIO host wakeup method suitable for the
platform and configurable GAP for host sleep handshake.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>