common: board_r: support enable_caches for RISC-V

The enable_caches is a generic hook for architecture-implemented, we
leverage this function to enable caches for RISC-V

Signed-off-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/arch/riscv/lib/cache.c b/arch/riscv/lib/cache.c
index b1d42bc..686e699 100644
--- a/arch/riscv/lib/cache.c
+++ b/arch/riscv/lib/cache.c
@@ -70,3 +70,7 @@
 {
 	return 0;
 }
+
+__weak void enable_caches(void)
+{
+}
diff --git a/common/board_r.c b/common/board_r.c
index e3e6248..630c245 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -114,7 +114,7 @@
 	return 0;
 }
 
-#ifdef CONFIG_ARM
+#if defined(CONFIG_ARM) || defined(CONFIG_RISCV)
 /*
  * Some of these functions are needed purely because the functions they
  * call return void. If we change them to return 0, these stubs can go away.
@@ -607,7 +607,7 @@
 	initr_trace,
 	initr_reloc,
 	/* TODO: could x86/PPC have this also perhaps? */
-#ifdef CONFIG_ARM
+#if defined(CONFIG_ARM) || defined(CONFIG_RISCV)
 	initr_caches,
 	/* Note: For Freescale LS2 SoCs, new MMU table is created in DDR.
 	 *	 A temporary mapping of IFC high region is since removed,