spl: Allow ATF to work when dcache is disabled

The dcache may not be enabled in SPL. Add a check to avoid trying to
use an undefined function.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

common/spl/spl_atf.c

@@ -204,7 +204,8 @@ static void __noreturn bl31_entry(uintptr_t bl31_entry, uintptr_t bl32_entry,
 						       fdt_addr);
 
 	raw_write_daif(SPSR_EXCEPTION_MASK);
-	dcache_disable();
+	if (!CONFIG_IS_ENABLED(SYS_DCACHE_OFF))
+		dcache_disable();
 
 	atf_entry(bl31_params, (void *)fdt_addr);
 }