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>

arch/arm/lib/cache-cp15.c

@@ -92,13 +92,18 @@ static inline void mmu_setup(void)
 	set_cr(reg | CR_M);
 }
 
+static int mmu_enabled(void)
+{
+	return get_cr() & CR_M;
+}
+
 /* cache_bit must be either CR_I or CR_C */
 static void cache_enable(uint32_t cache_bit)
 {
 	uint32_t reg;
 
 	/* The data cache is not active unless the mmu is enabled too */
-	if (cache_bit == CR_C)
+	if ((cache_bit == CR_C) && !mmu_enabled())
 		mmu_setup();
 	reg = get_cr();	/* get control reg. */
 	cp_delay();
@@ -117,7 +122,7 @@ static void cache_disable(uint32_t cache_bit)
 			return;
 		/* if disabling data cache, disable mmu too */
 		cache_bit |= CR_M;
-		flush_cache(0, ~0);
+		flush_dcache_all();
 	}
 	reg = get_cr();
 	cp_delay();

arch/arm/lib/cache.c

@@ -42,3 +42,14 @@ void  __flush_cache(unsigned long start, unsigned long size)
 }
 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")));