Polish the u-boot image recipe a bit

Make the image recipe for the minimal image just be 4G for easy
readability rather then a size in bytes. Also start the general
partition directly after the system one, making the layout internally
consistent. Potential future tweak would be to sync the uefi and the
u-boot layouts a bit more but that really has no big practical impact

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>

apertis-image-uboot.yaml

@@ -19,7 +19,7 @@ actions:
   - action: image-partition
     imagename: {{ $image }}
 {{ if eq $type "minimal" }}
-    imagesize: 4294967296
+    imagesize: 4G
 {{ else }}
     imagesize: 15G
 {{end}}
@@ -54,7 +54,7 @@ actions:
 {{ if eq $type "minimal" }}
         start: 1024M
 {{ else }}
-        start: 8672M
+        start: 8192M
 {{end}}
         end: -4M