vmbase: Move crosvm layout to aarch64

Crosvm provide architecture specific memory layout and set of peripheral devices. This commit move layout definition to aarch64 specific code directories as  a preparation before adding new CPU architecture.

Bug: 362733888
Test: m libvmbase

Change-Id: Ia8e82eb928d5fdc444581ca6fee145d2324a3591
diff --git a/libs/libvmbase/src/exceptions.rs b/libs/libvmbase/src/exceptions.rs
index b04cb16..5965bda 100644
--- a/libs/libvmbase/src/exceptions.rs
+++ b/libs/libvmbase/src/exceptions.rs
@@ -15,8 +15,8 @@
 //! Helper functions and structs for exception handlers.
 
 use crate::{
+    arch::aarch64::layout::UART_PAGE_ADDR,
     eprintln,
-    layout::UART_PAGE_ADDR,
     memory::{page_4kb_of, MemoryTrackerError, MEMORY},
     read_sysreg,
 };