stg-spec: Modify file paths according to new module hierarchy

This patch updates file paths according to new module hierarchy [1]:

  * GHC/Stg/Syntax.hs       <= stgSyn/StgSyn.hs
  * GHC/Types/Literal.hs    <= basicTypes/Literal.hs
  * GHC/Types/CostCentre.hs <= profiling/CostCentre.hs

This patch also updates old file path [2]:

  * utils/genapply/Main.hs  <= utils/genapply/GenApply.hs

[1]: https://gitlab.haskell.org/ghc/ghc/-/wikis/Make-GHC-codebase-more-modular
[2]: commit 0cc4aad3

[skip ci]