jtag: rewrite jim_jtag_configure() as COMMAND_HANDLER

The function is used for commands:
- jtag configure
- jtag cget

While there, add the missing .usage field.

Change-Id: I97ddc4898259ddb7fd2d057a997f33a6f4b0e2a8
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8058
Tested-by: jenkins

src/jtag/tcl.h

@@ -20,8 +20,7 @@
 
 #include <helper/command.h>
 
-int jim_jtag_configure(Jim_Interp *interp, int argc,
-		Jim_Obj * const *argv);
+__COMMAND_HANDLER(handle_jtag_configure);
 __COMMAND_HANDLER(handle_jtag_tap_enabler);
 
 #endif /* OPENOCD_JTAG_TCL_H */