Revert "sdcard_image-rpi.bbclass: rename boot partition to boot"
Revert "sdcard_image-rpi.bbclass: rename boot partition to boot"

* Naming boot partition by machine name is useful and does not break nothing
* It breaks our udev-rules hiding boot-partition

This reverts commit 0c2a8a135a65d6e13d5f20ac0a4f4e2b154a075d.

schnitzeltony/meta-raspi-light,schnitzeltony/meta-raspi-light