dtrace: additional action support (and bug fixes)

dtrace: additional action support (and bug fixes)

Removed ASSIST_* definitions because they are no longer necessary (though they
may come back in the future).

Changed the behaviour of DTrace in interrupt context to base it on in_irq()
rather than in_interrupt().

On Linux it is always safe to dereference current, so there is no need to do
special casing on various process-based DIF functions.  There is no need to
fake values coming from the 0-pid process.

Added curcpu variables.

Added d_path() function.  This takes a struct path and turns it into a string.

Renumbered the register IDs to match the xlator support at userspace, and to
also match the on-stack order of registers.

Have dtrace_getreg() operate on the task rather than just a set of registers,
because (in 64-bit mode) segment registers have their value stored in fields
in the process-specific task info.

Implemented the raise() action.

Changed the deadman interal to 10s, and timeout/user to 120s.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>