mips: unify prom_putchar() declarations

prom_putchar() is used centrally in early printk infrastructure therefore
at least MIPS should agree on the function return type.

[paul.burton@mips.com:
  - Include linux/types.h in asm/setup.h to gain the bool typedef before
    we start include asm/setup.h elsewhere.
  - Include asm/setup.h in all files that use or define prom_putchar().
  - Also standardise on signed rather than unsigned char argument.]

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19842/
Cc: linux-mips@linux-mips.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Jonas Gorski <jonas.gorski@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>

arch/mips/pic32/pic32mzda/early_console.c

@@ -13,6 +13,7 @@
  */
 #include <asm/mach-pic32/pic32.h>
 #include <asm/fw/fw.h>
+#include <asm/setup.h>
 
 #include "pic32mzda.h"
 #include "early_pin.h"
@@ -157,7 +158,7 @@ void __init fw_init_early_console(char port)
 	setup_early_console(port, baud);
 }
 
-int prom_putchar(char c)
+void prom_putchar(char c)
 {
 	if (console_port >= 0) {
 		while (__raw_readl(
@@ -166,6 +167,4 @@ int prom_putchar(char c)
 
 		__raw_writel(c, uart_base + U_TXR(console_port));
 	}
-
-	return 1;
 }