In the wake of the upcoming unification of the console setup code
between RPi3 and RPi4, extend the "clock-less" setup scheme to the
RPi3. This avoid programming any clocks or baud rate registers,
which makes the port more robust against GPU firmware changes.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ida83a963bb18a878997e9cbd55f8ceac6a2e1c1f

So far we have seen two different clock setups for the Raspberry Pi 4
board, with the VPU clock divider being different. This was handled by
reading the divider register and adjusting the base clock rate
accordingly.
Recently a new GPU firmware version appeared that changed the clock rate
*again*, though this time at a higher level, so the VPU rate (and the
apparent PLLC parent clock) did not seem to change, judging by reading
the clock registers.
So rather than playing cat and mouse with the GPU firmware or going
further down the rabbit hole of exploring the whole clock tree, let's
just skip the baud rate programming altogether. This works because the
GPU firmware actually sets up and programs the debug UART already, so
we can just use it.

Pass 0 as the base clock rate to let the console driver skip the setup,
also remove the no longer needed clock code.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ica88a3f3c9c11059357c1e6dd8f7a4d9b1f98fd7

The Raspberry Pi 4 is a single board computer with four Cortex-A72
cores. From a TF-A perspective it is quite similar to the Raspberry Pi
3, although it comes with more memory (up to 4GB) and has a GIC.

This initial port though differs quite a lot from the existing rpi3
platform port, mainly due to taking a much simpler and more robust
approach to loading the non-secure payload:
The GPU firmware of the SoC, which is responsible for initial platform
setup (including DRAM initialisation), already loads the kernel, device
tree and the "armstub" into DRAM. We take advantage of this, by placing
just a BL31 component into the armstub8.bin component, which will be
executed first, in AArch64 EL3.
The non-secure payload can be a kernel or a boot loader (U-Boot or
EDK-2), disguised as the "kernel" image and loaded by the GPU firmware.

So this is just a BL31-only port, which directly drops into EL2
and executes whatever has been loaded as the "kernel" image, handing
over the DTB address in x0.

Change-Id: I636f4d1f661821566ad9e341d69ba36f6bbfb546
Signed-off-by: Andre Przywara <andre.przywara@arm.com>