Documentation: sysfs-bus-usb: s/CONFIG_PM_RUNTIME/CONFIG_PM/

PM_RUNTIME has been replaced with PM by commit 464ed18e ("PM:
Eliminate CONFIG_PM_RUNTIME") hence substitute the reference on
PM_RUNTIME with PM and re-arrange the text to 80 column break.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>