[amd64] pool alloc/free clarify

src/arch/amd64/mm/pool.h

@@ -8,8 +8,8 @@
 /// Initialize the paging structure allocation pool
 void amd64_mm_pool_init(uintptr_t base, size_t size);
 
-/// Allocate a paging structure
+/// Allocate a paging structure (returns virtual addresses)
 uint64_t *amd64_mm_pool_alloc(void);
 
-/// Free a paging structure
+/// Free a paging structure (obj is a virtual pointer)
 void amd64_mm_pool_free(uint64_t *obj);