ar7: fix kernel builds for compiler test

TI AR7 Watchdog Timer is only build for 32bit.

Avoid error like:
In file included from drivers/watchdog/ar7_wdt.c:29:
./arch/mips/include/asm/mach-ar7/ar7.h: In function ‘ar7_is_titan’:
./arch/mips/include/asm/mach-ar7/ar7.h:111:24: error: implicit declaration of function ‘KSEG1ADDR’; did you mean ‘CKSEG1ADDR’? [-Werror=implicit-function-declaration]
  111 |  return (readl((void *)KSEG1ADDR(AR7_REGS_GPIO + 0x24)) & 0xffff) ==
      |                        ^~~~~~~~~
      |                        CKSEG1ADDR

Fixes: da2a68b ("watchdog: Enable COMPILE_TEST where possible")
Signed-off-by: Jackie Liu <[email protected]>
Reviewed-by: Guenter Roeck <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>

Author: JackieLiu1

drivers/watchdog/Kconfig

@@ -1664,7 +1664,7 @@ config SIBYTE_WDOG
 
 config AR7_WDT
 	tristate "TI AR7 Watchdog Timer"
-	depends on AR7 || (MIPS && COMPILE_TEST)
+	depends on AR7 || (MIPS && 32BIT && COMPILE_TEST)
 	help
 	  Hardware driver for the TI AR7 Watchdog Timer.