Fix installation of ghc-split (Trac #8760)

The rules weren't correctly setting INSTALL_TOPDIRS, and on top of that
the dependencies were wrong when BINDIST=YES.

Authored-by: Evan Hauck <khyperia@live.com>
Authored-by: Austin Seipp <austin@well-typed.com>
Signed-off-by: Austin Seipp <austin@well-typed.com>