passes all tests on two-processor smp

Includes code for TLB shootdown (which actually seems unnecessary for xv6)

locks were moved around.

memcpy directly.

this time do it ourselves instead of piggybacking on TLS.
add -fno-pic to Makefile; pic code breaks our fake TLS.

still not quite but a lot better.

 * rename c/cp to cpu/proc
 * rename cpu.context to cpu.scheduler
 * fix some comments
 * formatting for printout