target: introduce target_memory_ready() test

Use the new test in target memory access functions
instead of target_was_examined()

Drop the test from target_read/write_u8/16/32/64() helpers
as they directly call a memory access function which does
the test again.

Change-Id: Ic1753e461d2a4b91ce3a3e1bf3e86eb2be743d46
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/9178
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/target.h

@@ -590,6 +590,15 @@ int target_run_read_async_algorithm(struct target *target,
 		uint32_t entry_point, uint32_t exit_point,
 		void *arch_info);
 
+/**
+ * Returns true if target memory is ready to read/write.
+ *
+ * This routine is a wrapper for target->type->memory_ready.
+ * If the target specific check is not implemented,
+ * returns target_was_examined()
+ */
+bool target_memory_ready(struct target *target);
+
 /**
  * Read @a count items of @a size bytes from the memory of @a target at
  * the @a address given.