MAINTAINERS: list myself as maintainer for various Arm boards

In practice for most of the more-or-less orphan Arm board models,
I will review patches and put them in via the target-arm tree.
So list myself as an "Odd Fixes" status maintainer for them.

This commit downgrades these boards to "Odd Fixes":
 * Allwinner-A10
 * Exynos
 * Calxeda Highbank
 * Canon DIGIC
 * Musicpal
 * nSeries
 * Palm
 * PXA2xx

These boards were already "Odd Fixes":
 * Gumstix
 * i.MX31 (kzm)

Philippe Mathieu-Daudé has requested to be moved to R:
status for Gumstix now that I am listed as the M: contact.

Some boards are maintained, but their patches still go
via the target-arm tree, so add myself as a secondary
maintainer contact for those:
 * Xilinx Zynq
 * Xilinx ZynqMP
 * STM32F205
 * Netduino 2
 * SmartFusion2
 * Mecraft M2S-FG484
 * ASPEED BMCs
 * NRF51

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20181108134139.31666-1-peter.maydell@linaro.org