Use psci crate for PSCI calls.

Bug: 223166344
Test: Ran as unprotected VM bootloader under crosvm.
Change-Id: I8619f1b12fa63bcff581eeeb3ce3223b21cd793d
diff --git a/pvmfw/Android.bp b/pvmfw/Android.bp
index 5dbd4ec..3d77b2c 100644
--- a/pvmfw/Android.bp
+++ b/pvmfw/Android.bp
@@ -13,6 +13,7 @@
         "libcore.rust_sysroot",
     ],
     rustlibs: [
+        "libpsci",
         "libspin_nostd",
     ],
     enabled: false,