arm64: zynqmp: Add support for Avnet Ultra96

Avnet Ultra96 is rebranded Xilinx zcu100 revC/D. Add new defconfig files
and point to origin internal board name.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1bd583c..58b61ac 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -317,6 +317,7 @@
 F:	drivers/watchdog/cdns_wdt.c
 F:	include/zynqmppl.h
 F:	tools/zynqmp*
+N:	ultra96
 N:	zynqmp
 
 ARM ZYNQMP R5