add const keyword to some APIs

Add 'const' keyword to 'char *' parameters to allow command handlers to
pass constant string arguments.  These changes allow the 'args' command
handler to be changed to 'const' in a subsequent patch.

src/flash/flash.c

@@ -199,7 +199,7 @@ flash_bank_t *get_flash_bank_by_num(int num)
 }
 
 int flash_command_get_bank_by_num(
-	struct command_context_s *cmd_ctx, char *str, flash_bank_t **bank)
+	struct command_context_s *cmd_ctx, const char *str, flash_bank_t **bank)
 {
 	unsigned bank_num;
 	COMMAND_PARSE_NUMBER(uint, str, bank_num);

src/flash/flash.h

@@ -326,7 +326,7 @@ flash_bank_t *get_flash_bank_by_num(int num);
  * @returns ERROR_OK on success, or an error indicating the problem.
  */
 int flash_command_get_bank_by_num(struct command_context_s *cmd_ctx,
-		char *str, flash_bank_t **bank);
+		const char *str, flash_bank_t **bank);
 /**
  * Returns the flash bank like get_flash_bank_by_num(), without probing.
  * @param num The flash bank number.

src/flash/lpc2900.c

@@ -635,7 +635,7 @@ static int lpc2900_handle_read_custom_command( struct command_context_s *cmd_ctx
 
 	/* Try and open the file */
 	fileio_t fileio;
-	char *filename = args[1];
+	const char *filename = args[1];
 	int ret = fileio_open( &fileio, filename, FILEIO_WRITE, FILEIO_BINARY );
 	if( ret != ERROR_OK )
 	{
@@ -747,8 +747,8 @@ static int lpc2900_handle_write_custom_command( struct command_context_s *cmd_ct
 	image.base_address = 0;
 	image.start_address_set = 0;
 
-	char *filename = args[1];
-	char *type = (argc >= 3) ? args[2] : NULL;
+	const char *filename = args[1];
+	const char *type = (argc >= 3) ? args[2] : NULL;
 	retval = image_open(&image, filename, type);
 	if (retval != ERROR_OK)
 	{

src/flash/nand.c

@@ -304,7 +304,7 @@ nand_device_t *get_nand_device_by_num(int num)
 }
 
 int nand_command_get_device_by_num(struct command_context_s *cmd_ctx,
-		char *str, nand_device_t **device)
+		const char *str, nand_device_t **device)
 {
 	unsigned num;
 	COMMAND_PARSE_NUMBER(uint, str, num);

src/flash/nand.h

@@ -226,7 +226,7 @@ int nand_init(struct command_context_s *cmd_ctx);
 
 /// helper for parsing a nand device command argument string
 int nand_command_get_device_by_num(struct command_context_s *cmd_ctx,
-		char *str, nand_device_t **device);
+		const char *str, nand_device_t **device);
 
 
 #define		ERROR_NAND_DEVICE_INVALID		(-1100)