MAINTAINERS: Add some ARM related files to the corresponding sections

MAINTAINERS: Add some ARM related files to the corresponding sections

The files w/cpu/a*mpcore.c are already assigned to the ARM CPU
section, but the corresponding headers include/hw/cpu/a*mpcore.h
are still missing.

The file hw/*/imx* are already assigned to the i.MX31 machine, but
the corresponding header files include/hw/*/imx* are still missing.

The file hw/misc/arm_integrator_debug.c seems to belong to Integrator
CP, hw/cpu/realview_mpcore.c seems to belong to Real View, and
hw/misc/mst_fpga.c seems to belong to PXA2XX.

And the files hw/misc/zynq* and include/hw/misc/zynq* seem to belong
to the Xilinx Zynq machine.

Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>