[pvmfw][vmbase] Add constant PAGE_SIZE to vmbase

This cl adds a constant PAGE_SIZE of 4 KiB to vmbase and uses it
in pvmfw and rialto. Later it will be used as the page size in
the MemoryTracker for both pvmfw and rialto.

Bug: 284462758
Test: m pvmfw_img
Change-Id: I5b23f2571a3df81aa824f6f60e94b326fb1e225f
diff --git a/vmbase/src/memory/util.rs b/vmbase/src/memory/util.rs
index 3739d28..04d42cd 100644
--- a/vmbase/src/memory/util.rs
+++ b/vmbase/src/memory/util.rs
@@ -27,6 +27,9 @@
 /// The size of a 4MB memory in bytes.
 pub const SIZE_4MB: usize = 4 << 20;
 
+/// The page size in bytes assumed by vmbase - 4 KiB.
+pub const PAGE_SIZE: usize = SIZE_4KB;
+
 /// Reads the number of words in the smallest cache line of all the data caches and unified caches.
 #[inline]
 pub fn min_dcache_line_size() -> usize {