main/u-boot: Add fix for pbp panel not working on warm reset

After a warm reset, the display on a PBP doesn't work (although it does on a cold boot/reboot).

This patch works around the issue. It is part of an old series of 11 patches, the rest of which are all merged upstream:

https://gitlab.com/postmarketOS/pmaports/-/blob/512c02b1/device/community/u-boot-pinebookpro/0003-display-support.patch

The same patch is still around in Armbian, Tow-Boot and Manjaro:

• https://github.com/armbian/build/blob/8ebe1b9112547df1240aeb2f803bda85038a8700/patch/u-boot/u-boot-rockchip64/board-pinebook-pro-0005-panel-reset.patch
• https://github.com/Tow-Boot/Tow-Boot/blob/4531e25/boards/pine64-pinebookPro/0005-PBP-Fix-Panel-reset.patch
• https://gitlab.manjaro.org/manjaro-arm/packages/core/uboot-pinebookpro/-/blob/b5812973/0001-PBP-Fix-panel-reset.patch

With this patch the display works fine after a warm reboot. Sorry that I missed this on the original MR.