board: zynqmp: Fix for wrong AMS setting by ROM

A bug in the ZynqMP bootrom sets the PS_SYSMON_ANALOG_BUS register
at 0xFFA50914 to the wrong value 0x3201. This causes the AMS to
exchange the PS supply voltages 0 and 1. On Xilinx boards this is
not noticeable since these are tied together, it's only really
noticeable if banks 500 and 501 have different supplies. Xilinx' tech
support reported this undocumented register to be the cause, and
this patch applies a fix for all boards by programming the correct
value.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>