Take display offsets for PewPew M4 from the bootloader config

The PewPew M4 devices come with different displays, which require
different offsets. Since the information about offsets is saved in
the bootloader, we can take it from there.

ports/atmel-samd/boards/pewpew_m4/board.c

@@ -35,8 +35,36 @@
 
 displayio_fourwire_obj_t board_display_obj;
 
+typedef struct {
+    const uint32_t *config_data;
+    void *handoverHID;
+    void *handoverMSC;
+    const char *info_uf2;
+} UF2_BInfo;
+
+#define APP_START_ADDRESS 0x00004000
+#define UF2_BINFO ((UF2_BInfo *)(APP_START_ADDRESS - sizeof(UF2_BInfo)))
+
+#define CFG_DISPLAY_CFG0 39
+#define CFG_MAGIC0 0x1e9e10f1
+
 #define DELAY 0x80
 
+uint32_t lookupCfg(uint32_t key, uint32_t defl) {
+    const uint32_t *ptr = UF2_BINFO->config_data;
+    if (!ptr || (((uint32_t)ptr) & 3) || *ptr != CFG_MAGIC0) {
+        // no config data!
+    } else {
+        ptr += 4;
+        while (*ptr) {
+            if (*ptr == key)
+                return ptr[1];
+            ptr += 2;
+        }
+    }
+    return defl;
+}
+
 uint8_t display_init_sequence[] = {
     0x01, 0 | DELAY, 150, // SWRESET
     0x11, 0 | DELAY, 255, // SLPOUT
@@ -63,8 +91,6 @@ uint8_t display_init_sequence[] = {
               0x2E, 0x2C, 0x29, 0x2D,
               0x2E, 0x2E, 0x37, 0x3F,
               0x00, 0x00, 0x02, 0x10,
-    0x2a, 3, 0x02, 0x00, 0x81, // _CASET XSTART = 2, XEND = 129
-    0x2b, 3, 0x02, 0x00, 0x81, // _RASET XSTART = 2, XEND = 129
     0x13, 0 | DELAY, 10, // _NORON
     0x29, 0 | DELAY, 100, // _DISPON
 };
@@ -83,14 +109,17 @@ void board_init(void) {
         &pin_PA17, // TFT_RST Reset
         60000000);
 
+    uint32_t cfg0 = lookupCfg(CFG_DISPLAY_CFG0, 0x000000);
+    uint32_t offX = (cfg0 >> 8) & 0xff;
+    uint32_t offY = (cfg0 >> 16) & 0xff;
     displayio_display_obj_t* display = &displays[0].display;
     display->base.type = &displayio_display_type;
     common_hal_displayio_display_construct(display,
         bus,
         160, // Width (after rotation)
         128, // Height (after rotation)
-        0, // column start
-        0, // row start
+        offX, // column start
+        offY, // row start
         0, // rotation
         16, // Color depth
         false, // grayscale