sysfs.h: add BIN_ATTR macro

This makes it easier to create static binary attributes, which is needed
in a number of drivers, instead of "open coding" them.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>