sparc64: Add lightweight syscall mechanism for lwp_info

sparc64: Add lightweight syscall mechanism for lwp_info

This patch introduces a new "light weight" system call
mechanism which has the ability to retrieve small bits
of information and/or perform minor computations without
the need for a full blown save/switch/restore context.

Solaris provides _lwp_info(), which returns basically the
same information as getrusage(RUSAGE_THREAD) but much faster.
This is used extensively by the database code, and returns
the utime and stime for the calling thread.

(This patch also provides a fast getcpu function just as
a demonstration of how additional calls might be added.
Unlike x86, there is no unprivileged instruction to do this,
and so it is a fairly expensive system call.)

Orabug: 22952506

Signed-off-by: Rob Gardner <rob.gardner@oracle.com>