[Keyboard] Add: Initial steamvan firmware code (#6501)

* Add: Initial steamvan firmware code

* Apply suggestions from code review

Co-Authored-By: fauxpark <fauxpark@gmail.com>

* Update: Remove old macro commands, per reviewer comments

* Apply suggestions from code review

Co-Authored-By: noroadsleft <18669334+noroadsleft@users.noreply.github.com>

* Update: Remove redundant backlight struct

* Update: Replace preprocessor defines with enum

keyboards/handwired/steamvan/rev1/led_custom.h

@@ -0,0 +1,22 @@
+/*
+Copyright 2019 John M Daly <jmdaly@gmail.com>
+
+This program 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 2 of the License, or
+(at your option) any later version.
+
+This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+void backlight_task(void);
+void breathing_interrupt_disable(void);
+void breathing_interrupt_enable(void);