sim: Allow 'large-write' in mcuboot-sys

When collected together as a workspace, the test framework ends up
running all of the configurations on each project.  One configuration
option `large-write` doesn't really mean anything to mcuboot-sys, but
adding support for the feature allows this package to be tested along
with all of the other packages.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/mcuboot-sys/Cargo.toml b/sim/mcuboot-sys/Cargo.toml
index ffbce48..c678082 100644
--- a/sim/mcuboot-sys/Cargo.toml
+++ b/sim/mcuboot-sys/Cargo.toml
@@ -80,6 +80,9 @@
 # Check (in software) against version downgrades.
 downgrade-prevention = []
 
+# Large write.  Not meaningful, but present here so that the
+# full-suite tests will work for this configuration.
+large-write = []
 
 [build-dependencies]
 cc = "1.0.25"