Move stepper DAC to a separate file

Marlin/stepper_dac.h

@@ -0,0 +1,33 @@
+/*
+  stepper_dac.h   - To set stepper current via DAC
+
+  Part of Marlin
+
+  Copyright (c) 2016 MarlinFirmware
+
+  Marlin is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Marlin is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with Marlin.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef STEPPER_DAC_H
+#define STEPPER_DAC_H
+
+#include "dac_mcp4728.h"
+
+int dac_init();
+void dac_current_percent(uint8_t channel, float val);
+void dac_current_raw(uint8_t channel, uint16_t val);
+void dac_print_values();
+void dac_commit_eeprom();
+
+#endif // STEPPER_DAC_H