dtrace sdt: remove the ugly sname parameter of SDT_PROBE_DEFINE

In its stead use the Solaris / illumos approach of emulating '-' (dash)
in probe names with '__' (two consecutive underscores).

Reviewed by:	markj
MFC after:	3 weeks
sdt: add support for solaris/illumos style DTRACE_PROBE macros

The new macros are implemented in terms of SDT_PROBE_DEFINE and SDT_PROBE.
Probes defined in this way will appear under SDT provider named "sdt".
Parameter types are exposed via SDT_PROBE_ARGTYPE.
This is something that illumos does not have by default.

This kind of SDT probes is already present in ZFS code, so those probes
will now be available if KDTRACE_HOOKS options is enabled.

A potential future illumos compatibility enhancement is to encode a provider
name as a prefix in a probe name.

Reviewed by:	markj
MFC after:	3 weeks
X-MFC after:	r258622
Add a new debug section.
Add definitions for the microcode TLV flags entry (type 18.)

This isn't used anywhere just yet!

Obtained from:	Linux iwlwifi
opensolaris taskq: some cosmetic changes

- drop trailing whitespace
- remove redundant "extern" from function declarations
- remove unused macro

MFC after:	1 week
Mention that devd will kldload the driver when the device is connected.

Mention that the automatic mode switch from umass to u3g needed by some
devices does not work unless the driver is loaded before the device is
connected.

MFC after:	1 month