dtrace: add psinfo/cpuinfo OS level support

dtrace: add psinfo/cpuinfo OS level support

Added a member to the task structure, to hold DTrace specific process info.  It
stores (up to) the first 79 characters of the command line (with arguments),
as required for the pr_psargs elements in psinfo_t.  It also stores the number
of initial arguments (pr_argc), and the initial argument (pr_argv) and
environment variable (pr_envp) vectors.

This process information is pre-populated when an execve takes place in the
current task.  Note that if a process alters the arguments, this altertation
will be visible when pr_argv is consulted, and thus returned argument strings
may not match the originally provided values.

Enforce that invop handlers return a uint8 value, to be used in the future for
knowing what instruction to emulate upon return from an invop trap.

Added per-cpu CPU information that is used to provide cpuinfo_t data.

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