MAINTAINERS: Take maintainership for GPIO ACPI support

We will help Linus to maintain GPIO ACPI support.

Append a dedicated record to the MAINTAINERS data base.

Signed-off-by: Andy Shevchenko <[e-mail]>
Acked-by: Mika Westerberg <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

MAINTAINERS

···
 F:	include/uapi/linux/gpio.h
 F:	tools/gpio/
 
+GPIO ACPI SUPPORT
+M:	Mika Westerberg <[e-mail]>
+M:	Andy Shevchenko <[e-mail]>
+L:	[e-mail]
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/acpi/gpio-properties.txt
+F:	drivers/gpio/gpiolib-acpi.c
+
 GRE DEMULTIPLEXER DRIVER
 M:	Dmitry Kozlov <[e-mail]>
 L:	[e-mail]