minui: Move GRSurface into a class.

This CL adds GRSurface::Create() and dtor for managing the allocated
memory in GRSurface class. It also adds GRSurface::data() that hides the
underlying implementation, with both of const and non-const overloads.
This allows `const GRSurface&` to be more useful - previously it only
ensured a const member variable of `data`, instead of a read-only buffer
it points to.

It also marks the parameters in gr_texticon() and gr_blit() as const, as
they're incoming source that shouldn't be altered. It corrects the type
of gr_draw, which is the sink to be painted on (an earlier attempt was
made in [1], but didn't get the full picture correctly).

[1] https://android-review.googlesource.com/c/platform/bootable/recovery/+/704757/

Test: mmma -j bootable/recovery
Test: recovery_unit_test on marlin
Test: Run graphics test on marlin (fbdev).
Test: Run graphics test on blueline (drm).
Change-Id: I7904df084cd6c08fa04a9da97d01b4b1a6e3a20c
diff --git a/minui/graphics_adf.h b/minui/graphics_adf.h
index 2f019ed..099d329 100644
--- a/minui/graphics_adf.h
+++ b/minui/graphics_adf.h
@@ -14,21 +14,30 @@
  * limitations under the License.
  */
 
-#ifndef _GRAPHICS_ADF_H_
-#define _GRAPHICS_ADF_H_
+#pragma once
+
+#include <stdint.h>
 
 #include <adf/adf.h>
 
 #include "graphics.h"
+#include "minui/minui.h"
 
 class GRSurfaceAdf : public GRSurface {
+ public:
+  uint8_t* data() override {
+    return mmapped_buffer_;
+  }
+
  private:
+  friend class MinuiBackendAdf;
+
   int fence_fd;
   int fd;
   __u32 offset;
   __u32 pitch;
 
-  friend class MinuiBackendAdf;
+  uint8_t* mmapped_buffer_{ nullptr };
 };
 
 class MinuiBackendAdf : public MinuiBackend {
@@ -54,5 +63,3 @@
   unsigned int n_surfaces;
   GRSurfaceAdf surfaces[2];
 };
-
-#endif  // _GRAPHICS_ADF_H_