x86: soften multi-BAR mapping sanity check warning message

Impact: make debug warning less scary

The ioremap() time multi-BAR map warning has been causing false
positives:

  http://lkml.org/lkml/2008/12/10/432
  http://lkml.org/lkml/2008/12/11/136



So make it less scary by making it once-per-boot, by making it KERN_INFO
and by adding this text:

  "Info: mapping multiple BARs. Your kernel is fine."

Signed-off-by: Ingo Molnar <mingo@elte.hu>