Rename code_80069420.c -> z_memory_utils.c (#2314)

* Rename code_80069420.c -> z_memory.c

* z_memory -> z_memory_utils

src/code/z_memory_utils.c

@@ -0,0 +1,49 @@
+#include "ultra64.h"
+
+/**
+ * memcpy: copies `len` bytes from memory starting at `src` to memory starting at `dest`. Expects the memory
+ * specified by `src` and `dest` to not overlap.
+ *
+ * @see libultra also has a memcpy().
+ *
+ * @param dest address of start of buffer writing to
+ * @param src address of start of buffer to read from
+ * @param len number of bytes to copy. (`s32` rather than the standard `size_t`)
+ *
+ * @return dest
+ */
+void* MemCpy(void* dest, const void* src, s32 len) {
+    u8* d = dest;
+    const u8* s = src;
+
+    while (len > 0) {
+        *d++ = *s++;
+        len--;
+    }
+
+    return dest;
+}
+
+/**
+ * memset: sets `len` bytes to `val` starting at address `dest`.
+ *
+ * @see There are two other memsets in this codebase, Lib_MemSet(), memset().
+ * This one is unused.
+ *
+ * @param dest address to start at
+ * @param val value to write (`s32`, but interpreted as `u8`)
+ * @param len number of bytes to write. (`s32` rather than the standard `size_t`)
+ *
+ * @return dest
+ */
+void* MemSet(void* dest, s32 val, s32 len) {
+    u8* d = dest;
+    s32 s = len;
+
+    while (s > 0) {
+        *d++ = val;
+        s--;
+    }
+
+    return dest;
+}