MAINTAINERS: update Atmel AT91 entry

Add two co-maintainers and update the entry with new information.

Signed-off-by: Nicolas Ferre <[e-mail]>
Acked-by: Andrew Victor <[e-mail]>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <[e-mail]>
Cc: Russell King <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

MAINTAINERS

···
 L:	[e-mail] (moderated for non-subscribers)
 S:	Maintained
 
-ARM/ATMEL AT91RM9200 ARM ARCHITECTURE
+ARM/ATMEL AT91RM9200 AND AT91SAM ARM ARCHITECTURES
 M:	Andrew Victor <[e-mail]>
+M:	Nicolas Ferre <[e-mail]>
+M:	Jean-Christophe Plagniol-Villard <[e-mail]>
 L:	[e-mail] (moderated for non-subscribers)
 W:	http://maxim.org.za/at91_26.html
-S:	Maintained
+W:	http://www.linux4sam.org
+S:	Supported
+F:	arch/arm/mach-at91/
 
 ARM/BCMRING ARM ARCHITECTURE
 M:	Jiandong Zheng <[e-mail]>