feat(mm): initial mm work

src/mm/private.zig

@@ -0,0 +1,13 @@
+const config = @import("config");
+pub const phys = @import("phys.zig");
+pub const radix_pmap = @import("radix_pmap.zig");
+pub const pmap = @import("pmap.zig");
+pub const init = @import("init.zig");
+pub const PMap = pmap.PMap;
+
+pub const impl = if (@hasDecl(config, "CONFIG_ARCH_AMD64"))
+    @import("amd64/impl.zig")
+else
+    @compileError("unsupported architecture");
+
+pub var kernel_pmap: PMap = undefined;