sw:vec_iree: Update CMake variables to set HAL drivers

Match the change in https://github.com/google/iree/pull/7936

Change-Id: I083c82a6cc584e8c6369e68fe4da3538ba44330a

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd8264a..7070ba7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -44,7 +44,9 @@
 set(IREE_ENABLE_THREADING OFF)
 set(IREE_BUILD_TESTS OFF)
 set(IREE_BUILD_BINDINGS_TFLITE OFF)
-set(IREE_HAL_DRIVERS_TO_BUILD "Dylib_Sync;VMVX_Sync" CACHE STRING "IREE HAL Drivers" FORCE)
+set(IREE_HAL_DRIVER_DEFAULTS OFF CACHE BOOL "" FORCE)
+set(IREE_HAL_DRIVER_VMVX_SYNC ON CACHE BOOL "" FORCE)
+set(IREE_HAL_DRIVER_DYLIB_SYNC ON CACHE BOOL "" FORCE)
 
 #-------------------------------------------------------------------------------
 # IREE-specific definitions