tracing: Enable syscall optimization for MIPS

Since MIPS architecture has a sparse syscall array, select the
HAVE_SPARSE_SYSCALL_NR to save space.

Link: http://lkml.kernel.org/r/20191115234314.21599-2-hnaveed@wavecomp.com

Signed-off-by: Hassan Naveed <hnaveed@wavecomp.com>
Reviewed-by: Paul Burton <paulburton@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>