bloblist: Reduce blob-header size

The v0.9 spec provides for an 8-byte header for each blob, with fewer
fields.
The blob data start address should be aligned to the alignment specified
by the bloblist header.
Update the implementation to match this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Co-developed-by: Raymond Mao <raymond.mao@linaro.org>
Signed-off-by: Raymond Mao <raymond.mao@linaro.org>