* PACKAGE: add `libretro-scummvm-legacy` pkg
* PACKAGE-libretro-core-info: add scummvm-legacy info
* DEFCONFIG: add `libretro-scummvm-legacy` to shared builds
* BOARD: create gmenu2x's `scummvm.scummvm_legacy.ra` shortcut
* PACKAGE-libretro-scummvm: revert to mainstream & update ver. to working one 2.10.0
* PACKAGE-libretro-scummvm: use 'ScummVM` for system paths