sysfs: add initial support for binary files.

sysfs: add initial support for binary files.

Yes, binary files. But before you scream in angst, please realize that they
do have a marked purpose for exporting certain types of data from the kernel.

Basically, they are for exporting blobs of data that likely have some structure,
but that the kernel has no control over. This includes VPD data from device
headers, EDD data, or CPU microcode. Instead of parsing the data, then
formatting in a certain way, only so userspace can parse the data again, we
just shove it out in a binary blob to userspace, and let them deal with it.

Anyway, it defines a struct bin_attribute, with read() and write() methods
for the data. A read call should set the pointer in the sysfs_bin_buffer
object that is passed in.

A write call receives a buffer ptr, too, and must obey the count/offset
fields for correct data.