MAINTAINERS: update for semihostings new home

Seeing as I touched it I should at least keep an eye on it.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

MAINTAINERS

@@ -2562,6 +2562,13 @@ F: docs/pvrdma.txt
 F: contrib/rdmacm-mux/*
 F: qapi/rdma.json
 
+Semihosting
+M: Alex Bennée <alex.bennee@linaro.org>
+L: qemu-devel@nongnu.org
+S: Maintained
+F: hw/semihosting/
+F: include/hw/semihosting/
+
 Build and test automation
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 Build and test automation