* Bump Raspberry Pi kernel to 5.4
Bump kernel to the downstream Raspberry Pi 5.4 kernel. Drop patches
already merged upstream and use rebased patches for USB reset
controller (required for U-Boot 2020.10 for USB SSD boot).
* Add compatible node for upstream U-Boot
Add brcm,bcm2835-pl011 to make upstream U-Boot bind with the
bcm283x_pl011 driver. This allows to boot with the device tree provided
by the Raspberry Pi Linux kernel 5.4 even without enable_uart=1.
* Backport USB PCIe/XHCI patches to U-Boot 2020.07
Backport relevant patches required to make PCIe/USB XHCI work.
* Backport/integrate PCIe device tree changes from upstream Linux
U-Boot uses the device tree provided by upstream Linux. Make sure the
device tree has the relevant chanages to make VL805 USB controller
reset work.
* Document RPi 4 USB mass storage support (#746)
