arm: minor fixes for cache and mmu handling

1. make sure that page table setup is not done multiple times
2. flush_dcache_all() is more appropriate while disabling cache
   than a range flush on the entire memory(flush_cache())

   Provide a default implementation for flush_dcache_all()
   for backward compatibility and to avoid build issues.

Signed-off-by: Aneesh V <aneesh@ti.com>
diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
index dc3242c..92b61a2 100644
--- a/arch/arm/lib/cache.c
+++ b/arch/arm/lib/cache.c
@@ -42,3 +42,14 @@
 }
 void  flush_cache(unsigned long start, unsigned long size)
 	__attribute__((weak, alias("__flush_cache")));
+
+/*
+ * Default implementation:
+ * do a range flush for the entire range
+ */
+void	__flush_dcache_all(void)
+{
+	flush_cache(0, ~0);
+}
+void	flush_dcache_all(void)
+	__attribute__((weak, alias("__flush_dcache_all")));