locks: bakery: use is_dcache_enabled() helper

bakery_lock_normal.c uses the raw register accessor, read_sctlr(_el3)
to check whether the dcache is enabled.

Using is_dcache_enabled() is cleaner, and a good abstraction for
the library code like this.

A problem is is_dcache_enabled() is declared in the local header,
lib/xlat_tables_v2/xlat_tables_private.h

I searched for a good place to declare this helper. Moving it to
arch_helpers.h, closed to cache operation helpers, looks good enough
to me.

I also changed the type of 'is_cached' to bool for consistency,
and to avoid MISRA warnings.

Change-Id: I9b016f67bc8eade25c316aa9c0db0fa4cd375b79
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/include/arch/aarch32/arch_helpers.h b/include/arch/aarch32/arch_helpers.h
index cbac84b..a90b2a5 100644
--- a/include/arch/aarch32/arch_helpers.h
+++ b/include/arch/aarch32/arch_helpers.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -8,6 +8,7 @@
 #define ARCH_HELPERS_H
 
 #include <cdefs.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
 
@@ -178,6 +179,7 @@
 void flush_dcache_range(uintptr_t addr, size_t size);
 void clean_dcache_range(uintptr_t addr, size_t size);
 void inv_dcache_range(uintptr_t addr, size_t size);
+bool is_dcache_enabled(void);
 
 void dcsw_op_louis(u_register_t op_type);
 void dcsw_op_all(u_register_t op_type);