sandbox: bootm: Enable more bootm OS methods

It is useful for sandbox to build as much code as possible. Enable
support for booting various other operating systems. Add the missing
cache functions.

These operating systems do not actually boot on sandbox, of course.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
index a1c5c7c..d134905 100644
--- a/arch/sandbox/cpu/cpu.c
+++ b/arch/sandbox/cpu/cpu.c
@@ -286,6 +286,14 @@
 	enable_pci_map = enable;
 }
 
+void dcache_enable(void)
+{
+}
+
+void dcache_disable(void)
+{
+}
+
 int dcache_status(void)
 {
 	return 1;