Add support for the Xilinx Zynq Ultrascale+ MPSoC architecture (ZynqMP)
and the Xilinx ZCU104 board.

Barebox is booted as BL33 in EL-1 and expects that a BL2 (i.e. the FSBL)
already took care of initializing the RAM. Also for debug_ll, the UART
is expected to be already setup correctly. Thus, you have to add the
Barebox binary to a boot image as described in "Chapter 11: Boot and
Configuration" of "Zynq Ultrascale+ Device Technical Reference Manual".

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>