scroll_engine: Major rework to support pixel-based scrolling and scroll callbacks.

Much of the scrolling work is moved from lcd-bitmap-common to lcd-scroll.c,
a small scroll callback routine remains. This callback can potentially be
overridden by more extensive scrollers.

The callback also gets fed with pixel-based scrolling information, which
finally removes the strict line-based nature of the scroll engine. Along with
this is the change from scroll_stop_viewport_line() to scroll_stop_viewport_rect()
which works on a pixel-based rectangle instead of lines.

The ultimate goal is to move most of the scroll work to apps, which can
much better decide which line decorations to apply etc. This work is laying
the ground work.

Change-Id: I3b2885cf7d8696ddd9253d5a9a73318d3d42831a

apps/screen_access.c

@@ -247,9 +247,9 @@ struct screen screens[NB_SCREENS] =
         .scroll_delay=&lcd_scroll_delay,
         .clear_display=&lcd_clear_display,
         .clear_viewport=&lcd_clear_viewport,
+        .scroll_stop_viewport_rect=&lcd_scroll_stop_viewport_rect,
         .scroll_stop=&lcd_scroll_stop,
         .scroll_stop_viewport=&lcd_scroll_stop_viewport,
-        .scroll_stop_viewport_line=&lcd_scroll_stop_viewport_line,
         .update=&lcd_update,
         .update_viewport=&lcd_update_viewport,
         .backlight_on=&backlight_on,
@@ -348,9 +348,9 @@ struct screen screens[NB_SCREENS] =
         .scroll_delay=&lcd_remote_scroll_delay,
         .clear_display=&lcd_remote_clear_display,
         .clear_viewport=&lcd_remote_clear_viewport,
+        .scroll_stop_viewport_rect=&lcd_remote_scroll_stop_viewport_rect,
         .scroll_stop=&lcd_remote_scroll_stop,
         .scroll_stop_viewport=&lcd_remote_scroll_stop_viewport,
-        .scroll_stop_viewport_line=&lcd_remote_scroll_stop_viewport_line,
         .update=&lcd_remote_update,
         .update_viewport=&lcd_remote_update_viewport,
         .backlight_on=&remote_backlight_on,