Add cstr! macro

cstr!("X") is a shorthand for CStr::from_bytes_with_nul(b"X\0").unwrap()

Bug: 249054080
Test: TH

Change-Id: Iefdaa07179fe3b556fc9bc17595919ac93b7e569
diff --git a/pvmfw/src/dice.rs b/pvmfw/src/dice.rs
index 3ceb8ef..bad3453 100644
--- a/pvmfw/src/dice.rs
+++ b/pvmfw/src/dice.rs
@@ -14,6 +14,7 @@
 
 //! Support for DICE derivation and BCC generation.
 
+use crate::cstr;
 use crate::helpers::flushed_zeroize;
 use core::ffi::c_void;
 use core::ffi::CStr;
@@ -60,10 +61,9 @@
         self,
         salt: &[u8; HIDDEN_SIZE],
     ) -> diced_open_dice::Result<InputValues> {
-        let component_name = CStr::from_bytes_with_nul(b"vm_entry\0").unwrap();
         let mut config_descriptor_buffer = [0; 128];
         let config_descriptor_size = bcc_format_config_descriptor(
-            Some(component_name),
+            Some(cstr!("vm_entry")),
             None,  // component_version
             false, // resettable
             &mut config_descriptor_buffer,