Scarthgap support

Hi, we are currently porting GyroidOS to CVA6. We use this layer for basic hardware support. The corresponding changes to support Scarthgap which we made to this layer are part of this PR.

Following changes are included, see corresponding commit messages for detailed description:

• README: updated to scrathgap and poky
• tools/manifests/cva6-yocto: switch to poky and scarthgap versions
• recipes-games/vitetris: install binary as executable
• recipes-games/pacman4console: install binaries as executable
• recipes-games/pacman4console: fixed license text
• setup.sh: adapt to new {bblayers|local}.conf.sample files
• conf/templates/default: added local.conf.sample
• conf/templates/default: added bblayers.conf.sample
• conf/machine/cv64a6-genesys2: added bmap support
• conf/machine/cv32a6-genesys2: added bmap support
• recipes-kernel/linux/linux-yocto: switched to linux-yocto 6.6
• recipes-bsp/u-boot/u-boot-cva6: switched to mainline 2025.04
• recipes-bsp/opensbi: switched to generic platform
• Revert "patch openembedded core" and "apply patches in setup. sh"
• Revert "unify console management between agilex and genesys"
• recipes-core: removed changes to busybox
• conf/layer: bump version to scarthgap
• Revert "fix tools manifest" and "point to planvtech repo"