MAINTAINERS: Add myself as MStar/Sigmastar Armv7 SoC maintainers

As proposed by Daniel, I am going to help him to maintain the platform,
so add myself as co-maintainer.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
Acked-by: Daniel Palmer <daniel@thingy.jp>
Link: https://lore.kernel.org/r/20210910190322.27058-5-romain.perier@gmail.com'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -2236,6 +2236,7 @@ F:	arch/arm/mach-pxa/mioa701.c
 
 ARM/MStar/Sigmastar Armv7 SoC support
 M:	Daniel Palmer <daniel@thingy.jp>
+M:	Romain Perier <romain.perier@gmail.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 W:	http://linux-chenxing.org/