target: add target->type->has_mmu fn.

improve default target->read/write_phys_memory, produce
more sensible error messages if the mmu interface
functions have not been implemented yet vs. will
not be implemented(e.g. cortex m3).

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

src/target/cortex_m3.c

@@ -52,6 +52,12 @@ extern uint8_t armv7m_gdb_dummy_cpsr_value[];
 extern reg_t armv7m_gdb_dummy_cpsr_reg;
 #endif
 
+static int cortex_m3_has_mmu(struct target_s *target, bool *has_mmu)
+{
+	*has_mmu = false;
+	return ERROR_OK;
+}
+
 static int cortexm3_dap_read_coreregister_u32(swjdp_common_t *swjdp,
 		uint32_t *value, int regnum)
 {
@@ -1837,6 +1843,7 @@ target_type_t cortexm3_target =
 	.register_commands = cortex_m3_register_commands,
 	.target_create = cortex_m3_target_create,
 	.init_target = cortex_m3_init_target,
+	.has_mmu = cortex_m3_has_mmu,
 	.examine = cortex_m3_examine,
 };