surfansf28: More fixes:

* Use 16-bit audio output
 * More audio tweaks (mute on startup, working volume control)
 * Treat the rotary input as a scroll wheel (works now)

To-dos:

 * Better global keymap (incorporate touchscreen)
 * Turn on plugins and define the approximately eight bajillion keymaps
 * Still have some audible pops when we turn on, need to figure out why
 * Default Cabbiev2 comes off as rather crappy on this device

...I don't know how much work I will do on this thing, as the limited
number of physical controls (and a lack of a line-out) mean I'd never
want to use this thing myself.

Change-Id: I37229d92766495219ee989d9ae48b5ed79bd45f5

bootloader/hibyos_linux.c

@@ -98,6 +98,8 @@
 #define BUTTON_UP     BUTTON_PREV
 #define BUTTON_DOWN   BUTTON_NEXT
 #define BUTTON_SELECT BUTTON_PLAY
+#define BUTTON_LEFT   BUTTON_SCROLL_BACK
+#define BUTTON_RIGHT  BUTTON_SCROLL_FWD
 #include "bitmaps/hibyicon.h"
 #else
 #error "must define ICON_WIDTH/HEIGHT"