`tap_ctrl_rbb.c`: don't default to VM shutdown on quit (`Q`) command

[luismarques]

The OpenOCD BigBang protocol says:

An additional function, quit, is added to the remote_bitbang interface to
indicate there will be no more requests and the connection with the remote
driver should be closed.

I see no indication that such quit command should perform a target shutdown. It seems to only be intended to perform a connection shutdown (i.e., the "quit" refers to OpenOCD quitting, not the target / VM). Therefore, at least by default, the RBB shouldn't shutdown the VM. Let's change the "quit" property (controlling enable_quit) to default to false, once the scripts that depend on that have been properly updated.

diff --git a/hw/jtag/tap_ctrl_rbb.c b/hw/jtag/tap_ctrl_rbb.c
index 1a8363bc56..8f7978c971 100644
--- a/hw/jtag/tap_ctrl_rbb.c
+++ b/hw/jtag/tap_ctrl_rbb.c
@@ -626,7 +626,7 @@ static Property tap_ctrl_rbb_properties[] = {
     DEFINE_PROP_UINT32("idcode", TapCtrlRbbState, idcode, 0),
     DEFINE_PROP_UINT8("ir_length", TapCtrlRbbState, ir_length, 0),
     DEFINE_PROP_UINT8("idcode_inst", TapCtrlRbbState, idcode_inst, 1u),
-    DEFINE_PROP_BOOL("quit", TapCtrlRbbState, enable_quit, true),
+    DEFINE_PROP_BOOL("quit", TapCtrlRbbState, enable_quit, false),
     DEFINE_PROP_CHR("chardev", TapCtrlRbbState, chr),
     DEFINE_PROP_END_OF_LIST(),
 };