i2c: xgene-slimpro: include linux/io.h for memremap

The newly added support for the pcc mailbox fails to build
in some configurations:

drivers/i2c/busses/i2c-xgene-slimpro.c: In function 'xgene_slimpro_i2c_probe':
drivers/i2c/busses/i2c-xgene-slimpro.c:516:25: error: implicit declaration of function 'memremap'; did you mean 'memcmp'? [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-xgene-slimpro.c:518:13: error: 'MEMREMAP_WB' undeclared (first use in this function)
drivers/i2c/busses/i2c-xgene-slimpro.c:518:13: note: each undeclared identifier is reported only once for each function it appears in

This includes the missing header file.

Fixes: df5da47f ("i2c: xgene-slimpro: Add ACPI support by using PCC mailbox")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NHoan Tran <hotran@apm.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-xgene-slimpro.c

@@ -27,6 +27,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
+#include <linux/io.h>
 #include <linux/mailbox_client.h>
 #include <linux/module.h>
 #include <linux/of.h>