Remove PSCI monitor and firmware bits from sysutils/u-boot-rpi3
and switch it to using u-boot-master framework. Some patches are
required to make this work:
- Use old-style UART instead of new PL011 one. It requires "dtoverlay=pi3-disable-bt" line in config.txt
- Override fdt_addr_r if DTB is provided by firmware. This variable is hardcoded and if DTB address is changed via config.txt it's pointing to wrong address nad it confuses loader/kernel. And DTB address change is required, it should be set to 0x4000
- Increase console tick interval, otherwise UART polling hogs CPU and doesn't leave time for netbooting. See http://freebsd.1045724.x6.nabble.com/Raspberry-Pi-3-Network-Boot-tp6232887p6233938.html for details
- Remove PSCI monitor, it should be handled bu rpi-firmware port see https://reviews.freebsd.org/D14629 for details