arm: rpi: Add function to trigger VL805's firmware load

arm: rpi: Add function to trigger VL805's firmware load

On the Raspberry Pi 4, after a PCI reset, VL805's (a xHCI chip) firmware
may either be loaded directly from an EEPROM or, if not present, by the
SoC's VideCore (the SoC's co-processor). Introduce the function that
informs VideCore that VL805 may need its firmware loaded.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
[mszyprow: backport of https://patchwork.ozlabs.org/project/uboot/list/?series=174860&state=%2A&archive=both
 the final mainline patch depends on DTS changes not present in vendor tree]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I565a81e49c0684cfc2500ecb203ed4233cce4e14