Documentation: tweak the maintainers entry

The previous maintainer didn't want translation patches, but I'll happily
take them.  Also note a few subdirectories where the subsystem maintainers
would prefer to handle docs patches themselves.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

MAINTAINERS

@@ -3254,7 +3254,9 @@ S:	Maintained
 F:	Documentation/
 X:	Documentation/ABI/
 X:	Documentation/devicetree/
-X:	Documentation/[a-z][a-z]_[A-Z][A-Z]/
+X:	Documentation/acpi
+X:	Documentation/power
+X:	Documentation/spi
 T:	git git://git.lwn.net/linux-2.6.git docs-next
 
 DOUBLETALK DRIVER