Move boot image oatdump phony rules into Soong

The boot image oatdump rules depend on the details of dexpreopting
the boot image.  Instead of exporting all of the necessary values
to make, move the rules into build/soong/java/dexpreopt_bootjars.go
instead.  The output is now written to out/soong/boot.*.oatdump.txt.

Test: m dump-oat-boot
Change-Id: Ib10b53815b8b620bf205324f67c146526b75550e