vmbase: Move Trng internals to arch::aarch64

This commit moves trng implementation from common rand module to a
aarch64 arch module. This is at the moment purely cosmetic change,
however the purpose is move all aarch64 specific code away from common
modules to enable bringup of x86_64 support.

Bug: 362733888
Test: m pvmfw
Test: pVM boots with pvmfw
Change-Id: I5ac315ed38491de8b66f07a5df703cb50786c8bb
diff --git a/libs/libvmbase/src/entry.rs b/libs/libvmbase/src/entry.rs
index 5db0f25..5c74753 100644
--- a/libs/libvmbase/src/entry.rs
+++ b/libs/libvmbase/src/entry.rs
@@ -38,7 +38,7 @@
     // We keep a null byte at the top of the stack guard to act as a string terminator.
     let random_guard = &mut stack_guard[..(SIZE_OF_STACK_GUARD - 1)];
 
-    if let Err(e) = rand::init() {
+    if let Err(e) = crate::arch::rand::init() {
         panic!("Failed to initialize a source of entropy: {e}");
     }