ARM: samsung: fix PM debug build with DEBUG_LL but !MMU

Selecting CONFIG_SAMSUNG_PM_DEBUG (depending on CONFIG_DEBUG_LL) but
without CONFIG_MMU leads to build errors:

  arch/arm/plat-samsung/pm-debug.c: In function ‘s3c_pm_uart_base’:
  arch/arm/plat-samsung/pm-debug.c:57:2: error:
    implicit declaration of function ‘debug_ll_addr’ [-Werror=implicit-function-declaration]

Fixes: 99b2fc2b ("ARM: SAMSUNG: Use debug_ll_addr() to get UART base address")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200910154150.3318-1-krzk@kernel.org

arch/arm/plat-samsung/Kconfig

@@ -241,6 +241,7 @@ config SAMSUNG_PM_DEBUG
 	depends on PM && DEBUG_KERNEL
 	depends on PLAT_S3C24XX || ARCH_S3C64XX || ARCH_S5PV210
 	depends on DEBUG_EXYNOS_UART || DEBUG_S3C24XX_UART || DEBUG_S3C2410_UART
+	depends on DEBUG_LL && MMU
 	help
 	  Say Y here if you want verbose debugging from the PM Suspend and
 	  Resume code. See <file:Documentation/arm/samsung-s3c24xx/suspend.rst>