[pvmfw] Refactor MMIO range check in pvmfw

This cl refactors the MMIO range check and moves the
pvmfw-specific memory region constants out of MemoryTracker. This
simplifies the task of moving MemoryTracker to vmbase later.

Bug: 284462758
Test: m pvmfw_img
Change-Id: Ifb563215c59d7bb9dd4fae28bba68054b48b30d2
diff --git a/vmbase/src/layout/crosvm.rs b/vmbase/src/layout/crosvm.rs
index 66b9e44..fbeb477 100644
--- a/vmbase/src/layout/crosvm.rs
+++ b/vmbase/src/layout/crosvm.rs
@@ -16,5 +16,10 @@
 //!
 //! https://crosvm.dev/book/appendix/memory_layout.html#common-layout
 
+/// The start address of MMIO space.
+pub const MMIO_START: usize = 0x0;
+/// The end address of MMIO space.
+pub const MMIO_END: usize = 0x4000_0000;
+
 /// The start of the system's contiguous "main" memory.
 pub const MEM_START: usize = 0x8000_0000;