lib: utils: Add cache flush library

The current RISC-V CMO only defines how to flush a cache block. However,
certain use cases, such as power management, may require flushing the
entire cache. Therefore, a framework is being introduced to allow vendors
to flush the entire cache using their own methods.

Signed-off-by: Nick Hu <nick.hu@sifive.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20251020-cache-upstream-v7-1-69a132447d8a@sifive.com
Signed-off-by: Anup Patel <anup@brainfault.org>

lib/utils/cache/Kconfig

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: BSD-2-Clause
+
+menu "Cache Support"
+
+config CACHE
+	bool "Cache support"
+	default n
+
+endmenu