board: vexpress_ca9x4: Enable D-cache and MMU

Enable the D-cache, which will also enable the MMU.  The latter
make sure we don't do unaligned access on Strongly-ordered memory,
which has UNPREDICTABLE behaviour according the architecture
definition.  This fixes using U-Boot with recent versions of
QEMU's vexpress-ca9 emulation.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>

board/armltd/vexpress/vexpress_common.c

@@ -165,3 +165,11 @@ void smp_set_core_boot_addr(unsigned long addr, int corenr)
 	writel(addr, CONFIG_SYSFLAGS_ADDR);
 }
 #endif
+
+#if !CONFIG_IS_ENABLED(SYS_DCACHE_OFF)
+void enable_caches(void)
+{
+	/* Enable D-cache. I-cache is already enabled in start.S */
+	dcache_enable();
+}
+#endif