small tape support + turbo mode tweaks

src/kernal/board_u64/ultimate64_slow_fast.s

@@ -0,0 +1,22 @@
+;; #LAYOUT# STD *        #TAKE
+;; #LAYOUT# *   KERNAL_0 #TAKE
+;; #LAYOUT# *   *        #IGNORE
+
+
+!ifdef CONFIG_MB_U64 {
+
+U64_SLOW:
+
+	lda #$00                           ; for U64_TURBOCTL - badlines, 1MHz
+
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+U64_FAST:
+
+	lda #$0F                           ; for U64_TURBOCTL - badlines, 48MHz
+	sta SCPU_SPEED_TURBO               ; any value will do
+
+	rts
+}