Move .dynstr before _edata to fix image size calculation. The PE

Move .dynstr before _edata to fix image size calculation.  The PE
header contains an image size field that is calculated using the
difference between the start of the header and edata.  Since we
copy out .dynstr into the EFI binary, make sure that .dynstr is
before edata so that it's included in the image size.  This makes
it consistent with efiboot on armv7.

ok kettenis@