SDK: Rework repository-7.xsd

This changes the XML schema for repository-7 to put the
"full revision" in its own <revision> element with 4
sub-elements (major/minor/micro and preview).

Next step is to reuse this for min-[plat-]tools-rev
for dependencies.

Change-Id: I644f08e7383987682f8b0b31175ce58d02fd8751
28 files changed