Document eye textures as an enum

to clarify for `EnMd_UpdateEyes`

src/overlays/actors/ovl_En_Md/z_en_md.c

@@ -545,9 +545,9 @@ u8 EnMd_ShouldSpawn(EnMd* this, PlayState* play) {
 void EnMd_UpdateEyes(EnMd* this) {
     if (DECR(this->blinkTimer) == 0) {
         this->eyeIdx++;
-        if (this->eyeIdx > 2) {
+        if (this->eyeIdx > ENMD_EYE_CLOSED) {
             this->blinkTimer = Rand_S16Offset(30, 30);
-            this->eyeIdx = 0;
+            this->eyeIdx = ENMD_EYE_OPEN;
         }
     }
 }

src/overlays/actors/ovl_En_Md/z_en_md.h

@@ -27,6 +27,15 @@ typedef enum EnMdLimb {
     ENMD_LIMB_MAX
 } EnMdLimb;
 
+typedef enum EnMdEye {
+    ENMD_EYE_OPEN,
+    ENMD_EYE_HALF,
+    ENMD_EYE_CLOSED,
+    ENMD_EYE_ANGRY,
+    ENMD_EYE_LOOKING_UP,
+    ENMD_EYE_MAX
+} EnMdEye;
+
 typedef void (*EnMdActionFunc)(struct EnMd*, PlayState*);
 
 typedef struct EnMd {