don't produce overly large images

In the course of dealing with a problem in Xen's use of SeaBIOS when
the resulting image exceeds 128k I found it desirable to not add
unnecessarily much padding to the beginning of the image. Going in 64k
steps should be sufficient; perhaps one could use even smaller ones,
thus increasing the chances of there always being a window of available
space at C0000h.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/tools/checkrom.py
+++ b/tools/checkrom.py
@@ -32,11 +32,14 @@ def main():
     rawdata = f.read()
     f.close()
     datasize = len(rawdata)
-    finalsize = 64*1024
-    if datasize > 64*1024:
+    if datasize > 192*1024:
+        finalsize = 256*1024
+    elif datasize > 128*1024:
+        finalsize = 192*1024
+    elif datasize > 64*1024:
         finalsize = 128*1024
-        if datasize > 128*1024:
-            finalsize = 256*1024
+    else:
+        finalsize = 64*1024
 
     # Sanity checks
     start = symbols['code32flat_start'].offset