pvmfw: Integrate buddy_system_allocator

Add support for heap allocation.

Test: atest MicrodroidTestApp
Change-Id: I6b4df790b3cd86fe29db87dd312d5c671548e607
diff --git a/pvmfw/src/main.rs b/pvmfw/src/main.rs
index 870172d..c0bb263 100644
--- a/pvmfw/src/main.rs
+++ b/pvmfw/src/main.rs
@@ -16,10 +16,12 @@
 
 #![no_main]
 #![no_std]
+#![feature(default_alloc_error_handler)]
 
 mod avb;
 mod entry;
 mod exceptions;
+mod heap;
 mod helpers;
 mod mmio_guard;
 mod smccc;