sandbox: Migrate ARCH_MAP_SYSMEM to Kconfig

Move this from a hard-coded define in config.mk to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/Kconfig b/arch/sandbox/Kconfig
index f83282d..7606469 100644
--- a/arch/sandbox/Kconfig
+++ b/arch/sandbox/Kconfig
@@ -1,6 +1,9 @@
 menu "Sandbox architecture"
 	depends on SANDBOX
 
+config ARCH_MAP_SYSMEM
+	def_bool y
+
 config SYS_ARCH
 	default "sandbox"
 
diff --git a/arch/sandbox/config.mk b/arch/sandbox/config.mk
index 1f8cb61..2b1b657 100644
--- a/arch/sandbox/config.mk
+++ b/arch/sandbox/config.mk
@@ -2,7 +2,6 @@
 # Copyright (c) 2011 The Chromium OS Authors.
 
 PLATFORM_CPPFLAGS += -D__SANDBOX__ -U_FORTIFY_SOURCE
-PLATFORM_CPPFLAGS += -DCONFIG_ARCH_MAP_SYSMEM
 PLATFORM_CPPFLAGS += -fPIC
 PLATFORM_LIBS += -lrt
 SDL_CONFIG ?= sdl2-config