MAINTAINERS: Update Cavium ThunderX2 entry

Add Robert Richter as the primary maintainer for this platform.

Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index 5f03285..c1ae7f4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3176,6 +3176,7 @@
 F:	drivers/crypto/cavium/cpt/
 
 CAVIUM THUNDERX2 ARM64 SOC
+M:	Robert Richter <rrichter@cavium.com>
 M:	Jayachandran C <jnair@caviumnetworks.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained