Use psci crate for PSCI calls.

Bug: 223166344
Test: Ran as unprotected VM bootloader under crosvm.
Change-Id: I8619f1b12fa63bcff581eeeb3ce3223b21cd793d
diff --git a/pvmfw/src/main.rs b/pvmfw/src/main.rs
index d38b1e3..395c252 100644
--- a/pvmfw/src/main.rs
+++ b/pvmfw/src/main.rs
@@ -19,7 +19,6 @@
 
 mod console;
 mod exceptions;
-mod psci;
 mod uart;
 
 use core::panic::PanicInfo;
@@ -31,7 +30,7 @@
     console::init();
     println!("Hello world");
 
-    system_off();
+    system_off().unwrap();
     #[allow(clippy::empty_loop)]
     loop {}
 }
@@ -39,6 +38,6 @@
 #[panic_handler]
 fn panic(info: &PanicInfo) -> ! {
     eprintln!("{}", info);
-    system_reset();
+    system_reset().unwrap();
     loop {}
 }