Fix a handful of audit-related issue

This is sort of a mix between a new feature and a bug fix.  I've managed
to screw up merging this patch set a handful of times but I think it's
OK this time around.  The main new feature here is audit support for
RISC-V, with some fixes to audit-related bugs that cropped up along the
way:

* The addition of NR_syscalls into unistd.h, which is necessary for
  CONFIG_FTRACE_SYSCALLS.
* The definition of CREATE_TRACE_POINTS so
  __tracepoint_sys_{enter,exit} get defined.
* A fix for trace_sys_exit() so we can enable
  CONFIG_HAVE_SYSCALL_TRACEPOINTS.