UPSTREAM: util/riscvtools: Provide a tohost/fromhost symbols so Spike doesn't hang

See https://github.com/riscv/riscv-isa-sim/issues/54 for more
information.

BUG=None
BRANCH=None
TEST=None

Change-Id: I8cda8dc07866d395eb3ce5d94df8232840fa8b82
Original-Signed-off-by: Jonathan Neuschfer <j.neuschaefer@gmx.net>
Original-Reviewed-on: https://review.coreboot.org/15288
Original-Tested-by: build bot (Jenkins)
Original-Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/360811
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

util/riscvtools/spike-elf.ld

@@ -8,4 +8,8 @@ SECTIONS
 	.data : {
 		*(.data)
 	}
+
+	tohost = .;
+	. = . + 8;
+	fromhost = .;
 }