Ensure verify operation completed in full if chip memory modified

The patch adds new functionality to the test: tracking the areas of
chip memory that were modified (i.e. by erase or write operation),
and then checking those areas were completely covered by verify
operation.

The test operates over the mock chip memory of 16 bytes, so it is
possible to track each byte which was modified, and assert that is
has been verified afterwards.

Adding the test found a bug which is fixed in this commit:

Post-cleanup after processing unaligned region for the case when end
region needs to be extended to align with erase block. Writing was
done correctly, but post-processing of newcontents could cause
one-off offset at the end of the region, which would make
verification appear false-negative (see test cases #16-19).

Change-Id: I3c5d55a0deb20f23f4072caac8c0dce04cc98fd4
Signed-off-by: Anastasia Klimchuk <aklm@flashrom.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/84078
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Peter Marheine <pmarheine@chromium.org>

erasure_layout.c

@@ -399,7 +399,7 @@ _end:
 	}
 
 	if (old_end_buf) {
-		memcpy(newcontents + old_end, old_end_buf, end_buf_len);
+		memcpy(newcontents + old_end + 1, old_end_buf, end_buf_len);
 		free(old_end_buf);
 	}