pvmfw: helpers: Export SIZE_4KB

Test: -
Change-Id: I955a1504c8e976e2e9eeb968f6e08b2355de6a54
diff --git a/pvmfw/src/helpers.rs b/pvmfw/src/helpers.rs
index bcace14..ac3a48e 100644
--- a/pvmfw/src/helpers.rs
+++ b/pvmfw/src/helpers.rs
@@ -14,6 +14,8 @@
 
 //! Miscellaneous helper functions.
 
+pub const SIZE_4KB: usize = 4 << 10;
+
 /// Computes the address of the page containing a given address.
 pub const fn page_of(addr: usize, page_size: usize) -> usize {
     addr & !(page_size - 1)
@@ -30,7 +32,5 @@
 
 /// Computes the address of the 4KiB page containing a given address.
 pub const fn page_4kb_of(addr: usize) -> usize {
-    const PAGE_SIZE: usize = 4 << 10;
-
-    page_of(addr, PAGE_SIZE)
+    page_of(addr, SIZE_4KB)
 }