rockchip: add dkms and gcc for installing PineTab2 Wi-Fi driver

This was discussed during the last dev meeting and I have tested the change and also the size difference in the resulting images. Tl;dr: this change makes it possible to install the PineTab2 Wi-Fi driver on a newly installed system without ever having to connect to the internet to install dkms and gcc, the two deps for installing the driver.

According to the GNOME Disk Utility, a rockchip image including dkms and gcc is 200MB bigger than one without them. This is in the image itself though. Both locally-built images include free space, so I'm not sure how big the final difference is. Once 6.8 enters stable, including these two packages in the rockchip image will make installing the Wi-Fi driver and firmware a lot easier.

To be specific, it will make it possible to simply copy them to the SD card and install them after the OS (installation and) boot, without requiring an internet connection like you do now (to install dkms and gcc). If the license issue with the driver and firmware is fixed, then the driver and firmware could be included in a future image as well.

These two packages are prerequisites for that, and they make they make the current situation easier now.