Add types to build MAIR values.

These let a constant MAIR value be built with a builder pattern and
named constants, which should be more readable and safer than using
bitwise operations directly. Display implementations are also included
to format MAIR values in a human-readable form.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### New features
+
+- Added `mair` module with types to build MAIR values.
+
 ## 0.7.1
 
 ### New features

src/lib.rs

@@ -49,11 +49,12 @@
 pub mod idmap;
 #[cfg(feature = "alloc")]
 pub mod linearmap;
+pub mod mair;
 pub mod paging;
 #[cfg(feature = "alloc")]
 pub mod target;
 
-#[cfg(feature = "alloc")]
+#[cfg(any(test, feature = "alloc"))]
 extern crate alloc;
 
 #[cfg(target_arch = "aarch64")]