bloblist: Support initing from multiple places

bloblist: Support initing from multiple places

Typically the bloblist is set up after the devicetree is present. This
makes sense because bloblist may use malloc() to allocate the space it
needs.

However sometimes the devicetree itself may be present in the bloblist.
In that case it is at a known location in memory so we can init the
bloblist very early, before devicetree.

Add a flag to indicate whether the bloblist has been inited. Add a
function to init it only if needed. Use that in the init sequence.

Signed-off-by: Simon Glass <sjg@chromium.org>