pvmfw: Move aarch64 exceptions handling to new `arch` module

Due to incoming changes in libvmbase and pvmfw that will introduce new CPU architecture, there is necessary to separate code basing on platform. To achieve this new module/directory `arch` is introduced by this commit. This new module should be used as split point between architectures - new platform specific code should be only added behind `arch` module and exposed in platform independent way to the rest of the program.

Bug: 362733888
Test: m pvmfw

Change-Id: Ife352453563232d8313061a1ada844b01011a9bc
diff --git a/guest/pvmfw/src/main.rs b/guest/pvmfw/src/main.rs
index afa64e0..9c67be8 100644
--- a/guest/pvmfw/src/main.rs
+++ b/guest/pvmfw/src/main.rs
@@ -19,13 +19,13 @@
 
 extern crate alloc;
 
+mod arch;
 mod bcc;
 mod bootargs;
 mod config;
 mod device_assignment;
 mod dice;
 mod entry;
-mod exceptions;
 mod fdt;
 mod gpt;
 mod instance;