sandbox: Introduce Kconfig option for 32/64 bit host

It seems most of the time we are building and running sandbox on 64-bit host.
But we do support 32-bit host as well. Introduce Kconfig option for this.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/Kconfig

@@ -18,4 +18,21 @@ config SYS_CONFIG_NAME
 	default "sandbox_spl" if SANDBOX_SPL
 	default "sandbox" if !SANDBOX_SPL
 
+choice
+	prompt "Run sandbox on 32/64-bit host"
+	default SANDBOX_64BIT
+	help
+	  Sandbox can be built on 32-bit and 64-bit hosts.
+	  The default is to build on a 64-bit host and run
+	  on a 64-bit host. If you want to run sandbox on
+	  a 32-bit host, change it here.
+
+config SANDBOX_32BIT
+	bool "32-bit host"
+
+config SANDBOX_64BIT
+	bool "64-bit host"
+
+endchoice
+
 endmenu