Convert CONFIG_SYS_MEM_TOP_HIDE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MEM_TOP_HIDE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/samsung/common/board.c b/board/samsung/common/board.c
index 97791aa..ff178b7 100644
--- a/board/samsung/common/board.c
+++ b/board/samsung/common/board.c
@@ -107,9 +107,9 @@
 	}
 	boot_temp_check();
 #endif
-#ifdef CONFIG_TZSW_RESERVED_DRAM_SIZE
+#if CONFIG_VAL(SYS_MEM_TOP_HIDE)
 	/* The last few MB of memory can be reserved for secure firmware */
-	ulong size = CONFIG_TZSW_RESERVED_DRAM_SIZE;
+	ulong size = CONFIG_SYS_MEM_TOP_HIDE;
 
 	gd->ram_size -= size;
 	gd->bd->bi_dram[CONFIG_NR_DRAM_BANKS - 1].size -= size;