MAINTAINERS: Add NRF51 entry

This contains the NRF51, and the machine that uses it, the BBC
micro:bit.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NJoel Stanley <joel@jms.id.au>
Message-id: 20180831220920.27113-2-joel@jms.id.au
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

MAINTAINERS

@@ -671,6 +671,14 @@ F: include/hw/*/*aspeed*
 F: hw/net/ftgmac100.c
 F: include/hw/net/ftgmac100.h
 
+NRF51
+M: Joel Stanley <joel@jms.id.au>
+L: qemu-arm@nongnu.org
+S: Maintained
+F: hw/arm/nrf51_soc.c
+F: hw/arm/microbit.c
+F: include/hw/arm/nrf51_soc.h
+
 CRIS Machines
 -------------
 Axis Dev88