usb: core: Remove the useless struct usb_devmap which is just a bitmap

struct usb_devmap is really just a bitmap. No need to have a dedicated
structure for that.

Simplify code and use DECLARE_BITMAP() directly instead.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/1d818575ff7a1e8317674aecf761ee23c89fdc84.1714815990.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>