vendor: Add vmm-sys-util duplicate

Since the top-level Cargo.toml specifies a vmm-sys-util revision
but not the sub crates, Cargo.lock points at 2 different crates.
cargo vendor copies both of them into the vendor directory but
forces the build to use the one coming from the top level driven
requirement.

Although this is a waste of space, this is a cargo vendor limitation
that we have to live with for now.

Also, because the dependency onto linux-loader had to be updated,
we had to specify a newly introduced feature called "elf".

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vendor/git-bda1448fb2afcb00/linux-loader/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2018"
 license = "Apache-2.0 AND BSD-3-Clause"
 
 [features]
-default = ["elf"]
+default = []
 elf = []
 bzImage = []