Add kelvin patched riscv toolchain option

This is for supporting CI/pre-submit and general regression test setup.

Change-Id: I62fb103328df676e65f9cbd126ad47af06906632

install-toolchain.sh

diff --git a/install-toolchain.sh b/install-toolchain.sh
index 72efcb7..e13a48f 100755
--- a/install-toolchain.sh
+++ b/install-toolchain.sh
@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Install the prebuilt RISC-V GCC/LLVM toolchain.
+# Install the prebuilt RISC-V GCC/LLVM/Kelvin toolchain.
 
 function clean {
   if [[ ! -f "${PREINSTALL_DIR}/${TOOLCHAIN_TARBALL}" ]]; then
@@ -39,7 +39,7 @@
 if [[ -z "$1" ]]; then
   cat << EOM
 Usage: install-toolchain.sh target
-Where target is gcc or llvm
+Where target is gcc, llvm, or kelvin
 EOM
   exit 1
 fi
@@ -54,6 +54,9 @@
   llvm)
     TOOLCHAIN_TARBALL="toolchain_iree_rv32.tar.gz"
     ;;
+  kelvin)
+    TOOLCHAIN_TARBALL="toolchain_kelvin.tar.gz"
+    ;;
 
   *)
     echo "unsupported target: ${TARGET}"