armv7m: cache: add mmu_set_region_dcache_behaviour() stub for compatibility

Since some driver requires this function add it as an empty stub
when DCACHE is OFF.
Signed-off-by: NGiulio Benetti <giulio.benetti@benettiengineering.com>

arch/arm/cpu/armv7m/cache.c

@@ -291,6 +291,12 @@ void flush_dcache_all(void)
 void invalidate_dcache_all(void)
 {
 }
+
+void mmu_set_region_dcache_behaviour(phys_addr_t start, size_t size,
+				     enum dcache_option option)
+{
+}
+
 #endif
 
 #if !CONFIG_IS_ENABLED(SYS_ICACHE_OFF)