arch: cache: cp15: Add mmu_set_region_dcache_behaviour() when SYS_DCACHE_OFF is enable

Fix following compilation issue when SYS_DCACHE_OFF is enable:
drivers/misc/scmi_agent.c:128: undefined reference to `mmu_set_region_dcache_behaviour'

when SYS_DCACHE_OFF is enable, mmu_set_region_dcache_behaviour() must be
defined.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/arch/arm/lib/cache-cp15.c b/arch/arm/lib/cache-cp15.c
index aab1bf4..0893915 100644
--- a/arch/arm/lib/cache-cp15.c
+++ b/arch/arm/lib/cache-cp15.c
@@ -93,12 +93,6 @@
 	mmu_page_table_flush(startpt, stoppt);
 }
 
-void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
-				     enum dcache_option option)
-{
-	mmu_set_region_dcache_behaviour_phys(start, start, size, option);
-}
-
 __weak void dram_bank_mmu_setup(int bank)
 {
 	struct bd_info *bd = gd->bd;
@@ -311,6 +305,12 @@
 {
 	return 0;					/* always off */
 }
+
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option)
+{
+}
+
 #else
 void dcache_enable(void)
 {
@@ -326,4 +326,10 @@
 {
 	return (get_cr() & CR_C) != 0;
 }
+
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option)
+{
+	mmu_set_region_dcache_behaviour_phys(start, start, size, option);
+}
 #endif