Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update the names of some member variables in comments to refect reality.
Apparently this was forgotten when this code was derived from the BSD
openprom(4).

Start each of the license/copyright comments with /*-, minor shuffle of lines

- Move OFW_NAME_MAX, used as a limit for OFW property names and device
identifiers, to openfirmio.h as OFIOCMAXNAME, so programs can use it
for buffer sizes etc.
Note: Although this is only a rough upper limit to make the code more
robust and to prevent the allocation of ridiculous amounts of memory,
the current limit of one page (8191 + '\0' in openfirm_getstr()) still
appears a bit high. The maximum length of OFW property names is 31.
I didn't find a maximum length for the device identifiers in the OFW
documentation but it certainly is much smaller than 8191, too.
- Enable the OFIOCSET ioctl, i.e. move it out from under #if 0.
- Don't use openfirm_getstr() for the property value in OFIOCSET, there
are also properties whose values aren't strings and it makes sense to
use a different maximum length for property values than OFW_NAME_MAX/
OFIOCMAXNAME. The maximum accepted property value is defined in
openfirmio.h as OFIOCMAXVALUE (currently the maximum size of the value
of the nvramrc property).
- Make OFIOCSET not return EINVAL when OF_setprop() returns a different
length for the written value than it was told to write, this is normal
for the text string values of the properties in the OFW /options node.
Instead, only return EINVAL if OF_setprop() returned -1 (value could
not be written or property could not be created). Add a comment about
the specialty of the OFW /options node.
- Make OFIOCSET return the length of the written value returned by
OF_setprop(), just like OF_getprop() does. Quite useful, at least for
debugging.

Reviewed by: tmm

Remove advertising clause from University of California Regent's
license, per letter dated July 22, 1999 and email from Peter Wemm,
Alan Cox and Robert Watson.

Approved by: core, peter, alc, rwatson

- Add an OFIOCGETPROPLEN ioctl() to get the length of a property.
- Do not use a fixed major.
- Minor cleanups.

Add a pseudo device which allows to access the OpenFirmware device tree
via ioctl()s. This was ported from NetBSD and adapted a bit to better
match our OpenFirmware support code.