arm: caches: add DCACHE_DEFAULT_OPTION

Add the new flags DCACHE_DEFAULT_OPTION to define the default
option to use according the compilation flags
CONFIG_SYS_ARM_CACHE_*.

This new compilation flag allows to simplify dram_bank_mmu_setup()
and can be used as third parameter (option=dcache option to select)
of mmu_set_region_dcache_behaviour function.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/lib/cache-cp15.c b/arch/arm/lib/cache-cp15.c
index 54509f1..d151441 100644
--- a/arch/arm/lib/cache-cp15.c
+++ b/arch/arm/lib/cache-cp15.c
@@ -99,15 +99,8 @@
 	for (i = bd->bi_dram[bank].start >> MMU_SECTION_SHIFT;
 	     i < (bd->bi_dram[bank].start >> MMU_SECTION_SHIFT) +
 		 (bd->bi_dram[bank].size >> MMU_SECTION_SHIFT);
-	     i++) {
-#if defined(CONFIG_SYS_ARM_CACHE_WRITETHROUGH)
-		set_section_dcache(i, DCACHE_WRITETHROUGH);
-#elif defined(CONFIG_SYS_ARM_CACHE_WRITEALLOC)
-		set_section_dcache(i, DCACHE_WRITEALLOC);
-#else
-		set_section_dcache(i, DCACHE_WRITEBACK);
-#endif
-	}
+	     i++)
+		set_section_dcache(i, DCACHE_DEFAULT_OPTION);
 }
 
 /* to activate the MMU we need to set up virtual memory: use 1M areas */