target/armv8: regularly send keep_alive packet.

Flushing all d-cache may be a long operation.
We need to send keep_alive regularly to keep the connection alive.
If not done a warning is emitted.

Change-Id: I52c3ee9a9f9b8a1dc0b8d5439e8b71212f56165a
Signed-off-by: Adrien Grassein <[email protected]>
Signed-off-by: Adrien Charruel <[email protected]>
Reviewed-on: https://review.openocd.org/c/openocd/+/8659
Reviewed-by: Antonio Borneo <[email protected]>
Tested-by: jenkins

Author: Adrien Grassein

src/target/armv8_cache.c

@@ -61,6 +61,7 @@ static int armv8_cache_d_inner_flush_level(struct armv8_common *armv8, struct ar
 				goto done;
 			c_way -= 1;
 		} while (c_way >= 0);
+		keep_alive();
 		c_index -= 1;
 	} while (c_index >= 0);