Regression from commit:
  loader/linux: do not pad initrd with zeroes at the end
  a8c47328

Wimboot fails since the change above because it expects the "trailer"
initrd element on an aligned address.
This issue shows only when newc_name is used and the last initrd
entry has a not aligned size.

Syslinux memdisk is using initrd image and needs to know uncompressed
size in advance. For gzip uncompressed size is at the end of compressed
stream. Grub padded each input file to 4 bytes at the end, which means
syslinux got wrong size.

Linux initramfs loader apparently does not care about trailing alignment.
So change code to align beginning of each file instead which atomatically
gives us the correct size for single file.
Reported-By: David Shaw <dshaw@jabberwocky.com>

Signed-off-by: Fu Wei <fu.wei@linaro.org>

	Just "packed" doesn't always pack the way we expect.

	rather than printf.