MIPS: ralink: Don't use "proxy" headers

Update header inclusions to follow IWYU (Include What You Use)
principle.

Fixes: 5804be061848 ("MIPS: ralink: Remove unused of_gpio.h")
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Andy Shevchenko <[e-mail]>
Acked-by: Sergio Paracuellos <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/ralink/timer.c

···
  * Copyright (C) 2013 John Crispin <[e-mail]>
 */
 
-#include <linux/platform_device.h>
-#include <linux/interrupt.h>
-#include <linux/timer.h>
+#include <linux/bits.h>
 #include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/timer.h>
+#include <linux/types.h>
 
 #include <asm/mach-ralink/ralink_regs.h>