powerpc: fix build when CONFIG_BOOKE_WDT is enabled

Commit ae3a197e (Disintegrate asm/system.h for PowerPC) broke build of
assembly files when CONFIG_BOOKE_WDT is enabled as follows:

  AS      arch/powerpc/lib/string.o
/home/baruch/git/stable/arch/powerpc/include/asm/reg_booke.h: Assembler messages:
/home/baruch/git/stable/arch/powerpc/include/asm/reg_booke.h:19: Error: Unrecognized opcode: `extern'
/home/baruch/git/stable/arch/powerpc/include/asm/reg_booke.h:20: Error: Unrecognized opcode: `extern'

Since setup_32.c is the only user of the booke_wdt configuration variables, move
the declarations there.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/include/asm/reg_booke.h

@@ -15,11 +15,6 @@
 #ifndef __ASM_POWERPC_REG_BOOKE_H__
 #define __ASM_POWERPC_REG_BOOKE_H__
 
-#ifdef CONFIG_BOOKE_WDT
-extern u32 booke_wdt_enabled;
-extern u32 booke_wdt_period;
-#endif /* CONFIG_BOOKE_WDT */
-
 /* Machine State Register (MSR) Fields */
 #define MSR_GS		(1<<28) /* Guest state */
 #define MSR_UCLE	(1<<26)	/* User-mode cache lock enable */

arch/powerpc/kernel/setup_32.c

@@ -150,6 +150,9 @@ notrace void __init machine_init(u64 dt_ptr)
 }
 
 #ifdef CONFIG_BOOKE_WDT
+extern u32 booke_wdt_enabled;
+extern u32 booke_wdt_period;
+
 /* Checks wdt=x and wdt_period=xx command-line option */
 notrace int __init early_parse_wdt(char *p)
 {