pvmfw: helpers: Introduce SIZE_2MB

Test: atest MicrodroidTestApp
Change-Id: I7175d7c166937d546beef0d7818deb7b2ca0e509
diff --git a/pvmfw/src/helpers.rs b/pvmfw/src/helpers.rs
index cade62e..adfc189 100644
--- a/pvmfw/src/helpers.rs
+++ b/pvmfw/src/helpers.rs
@@ -14,8 +14,8 @@
 
 //! Miscellaneous helper functions.
 
-pub const FDT_MAX_SIZE: usize = 2 << 20;
 pub const SIZE_4KB: usize = 4 << 10;
+pub const SIZE_2MB: usize = 2 << 20;
 
 /// Computes the address of the page containing a given address.
 pub const fn page_of(addr: usize, page_size: usize) -> usize {