MAINTAINERS: Declare tools/zynqmp* as Xilinx maintained

The zynqmpimage.c and the new zynqmpbif.c files are all maintained by
Xilinx for the Zynq platforms. Let's match them accordingly
in the MAINTAINERS file.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 031f7ea..c2ae68c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -292,7 +292,7 @@
 F:	drivers/usb/host/ehci-zynq.c
 F:	drivers/watchdog/cdns_wdt.c
 F:	include/zynqmppl.h
-F:	tools/zynqimage.c
+F:	tools/zynqmp*
 N:	zynqmp
 
 BUILDMAN