linux-postmarketos-exynos5: add package

This adds a kernel package for exynos5 devices. Config has been based on linux-postmarketos-exynos4's config and Hardkernel's odroid xu4 config.

New device odroid-xu4 is added which uses it. It is similar to odroid-hc2, and could use the same firmware package, but I opted for the slightly newer blobs from the 2020.01 branch in Hardkernel's repo.

Initial dtbs for Samsung-chagallwifi and samsung-klimtlte are also added, and a mainline kernel option added for the devices. The initial dtbs support:

• Installing PostmarketOS to internal, or external, storage
• Usb networking
• Getting logs over UART

samsung-chagallwifi patches have been sent to samsung-soc mailing list.