usb: Make USB persist default configurable

Commit 9214d1d8 set the USB persist flag as a default for all devices.
This might be desirable for some distributions, but it certainly has its
trade-offs... most importantly, it can significantly increase system
resume time, because the kernel blocks on resuming (and sometimes
resetting) USB devices before it unfreezes userspace.

This patch introduces a new config option CONFIG_USB_DEFAULT_PERSIST,
which allows distributions to make this decision on their own without
the need to carry a custom patch or revert the kernel's setting in
userspace.

[edited the Kconfig help text a bit - gregkh]

Signed-off-by: Julius Werner <jwerner@chromium.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>