ARM720: help/usage updates

Deprecate the "pass an instruction opcode" flavor of cp15 access
in favor of the "arm mcr ..." and "arm mrc ..." commands, which
offer fewer ways to break things.

Use the same EBNF syntax in the code as for the user's guide.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

doc/openocd.texi

@@ -5921,9 +5921,13 @@ which are implementations of the ARMv4T architecture
 based on the ARM7TDMI-S integer core.
 They are available in addition to the ARM and ARM7/ARM9 commands.
 
-@deffn Command {arm720t cp15} regnum [value]
+@deffn Command {arm720t cp15} opcode [value]
-Display cp15 register @var{regnum};
+@emph{DEPRECATED -- avoid using this.
+Use the @command{arm mrc} or @command{arm mcr} commands instead.}
+
+Display cp15 register returned by the ARM instruction @var{opcode};
 else if a @var{value} is provided, that value is written to that register.
+The @var{opcode} should be the value of either an MRC or MCR instruction.
 @end deffn
 
 @subsection ARM9 specific commands

src/target/arm720t.c

@@ -516,8 +516,10 @@ static const struct command_registration arm720t_exec_command_handlers[] = {
 		.name = "cp15",
 		.handler = arm720t_handle_cp15_command,
 		.mode = COMMAND_EXEC,
-		.usage = "<opcode> [value]",
+		/* prefer using less error-prone "arm mcr" or "arm mrc" */
-		.help = "display/modify cp15 register",
+		.help = "display/modify cp15 register using ARM opcode"
+			" (DEPRECATED)",
+		.usage = "instruction [value]",
 	},
 	COMMAND_REGISTRATION_DONE
 };