jtag: rewrite jim_jtag_tap_enabler() as COMMAND_HANDLER

The function is used for commands:
- jtag tapisenabled
- jtag tapenable
- jtag tapdisable

While there, add the missing .help and .usage fields and fix the
incorrect check in jtag_tap_enable() and jtag_tap_disable().

Change-Id: I0e1c9f0b8d9fbad19d09610a97498bec8003c27e
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7554
Tested-by: jenkins

src/target/adi_v5_dapdirect.c

@@ -89,12 +89,18 @@ static const struct command_registration dapdirect_jtag_subcommand_handlers[] =
 	{
 		.name = "tapisenabled",
 		.mode = COMMAND_EXEC,
-		.jim_handler = jim_jtag_tap_enabler,
+		.handler = handle_jtag_tap_enabler,
+		.help = "Returns a Tcl boolean (0/1) indicating whether "
+			"the TAP is enabled (1) or not (0).",
+		.usage = "tap_name",
 	},
 	{
 		.name = "tapenable",
 		.mode = COMMAND_EXEC,
-		.jim_handler = jim_jtag_tap_enabler,
+		.handler = handle_jtag_tap_enabler,
+		.help = "Try to enable the specified TAP using the "
+			"'tap-enable' TAP event.",
+		.usage = "tap_name",
 	},
 	{
 		.name = "tapdisable",