vmbase: Assert TCR_EL1 assumptions in Rust

Instead of documenting the assumption in a comment, check it at runtime
so that breaking changes may be automatically caught.

Note: no functional change intended.

Test: m pvmfw_img
Change-Id: Ib1a013b383997269de6a35762a041ef2a7df0ebb
diff --git a/vmbase/src/memory/dbm.rs b/vmbase/src/memory/dbm.rs
index 333d3f6..a7118bb 100644
--- a/vmbase/src/memory/dbm.rs
+++ b/vmbase/src/memory/dbm.rs
@@ -14,7 +14,7 @@
 
 //! Hardware management of the access flag and dirty state.
 
-use super::page_table::{is_leaf_pte, PT_ASID};
+use super::page_table::{is_leaf_pte, PageTable};
 use super::util::flush_region;
 use crate::{dsb, isb, read_sysreg, tlbi, write_sysreg};
 use aarch64_paging::paging::{Attributes, Descriptor, MemoryRegion};
@@ -91,7 +91,7 @@
         // An ISB instruction is required to ensure the effects of completed TLB maintenance
         // instructions are visible to instructions fetched afterwards.
         // See ARM ARM E2.3.10, and G5.9.
-        tlbi!("vale1", PT_ASID, va_range.start().0);
+        tlbi!("vale1", PageTable::ASID, va_range.start().0);
         dsb!("ish");
         isb!();
         Ok(())