pvmfw: Move aarch64 fn `jump_to_payload` to a separate module

Each architecture have its own boot protocole, so there is non generic way of implementing function `jump_to_payload(..)` in pvmfw for each platform. This commit move aarch64 specific logic to separate module hechaind `arch/aarch64` directories.

Bug: 354116267
Test: m pvmfw & boot payload

Change-Id: Ibac59fc1106c8f058fc35ff670d99e08567043cd
diff --git a/guest/pvmfw/src/arch.rs b/guest/pvmfw/src/arch.rs
index b9ab3a8..1bbf4d4 100644
--- a/guest/pvmfw/src/arch.rs
+++ b/guest/pvmfw/src/arch.rs
@@ -16,3 +16,6 @@
 
 #[cfg(target_arch = "aarch64")]
 mod aarch64;
+
+#[cfg(target_arch = "aarch64")]
+pub use aarch64::payload;