usb: core: make default autosuspend delay configurable

Make the default autosuspend delay configurable at build time.
This is useful for systems that require a non-standard value as
it avoids relying on the command line being properly set.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>