Add missing MemoryMap and MemoryRegionType imports

blog/content/second-edition/posts/09-paging-implementation/index.md

@@ -852,6 +852,8 @@ In order to create new page tables, we need to create a proper frame allocator.
 ```rust
 // in src/memory.rs
 
+use bootloader::bootinfo::MemoryMap;
+
 /// A FrameAllocator that returns usable frames from the bootloader's memory map.
 pub struct BootInfoFrameAllocator {
     memory_map: &'static MemoryMap,
@@ -886,6 +888,8 @@ Before we implement the `FrameAllocator` trait, we add an auxiliary method that
 ```rust
 // in src/memory.rs
 
+use bootloader::bootinfo::MemoryRegionType;
+
 impl BootInfoFrameAllocator {
     /// Returns an iterator over the usable frames specified in the memory map.
     fn usable_frames(&self) -> impl Iterator<Item = PhysFrame> {