cmd history: Match history buffer size to console buffer

Match history buffer size to console buffer size. History buffer size
was hard coded to 256, artificially limiting the command buffer size.
The history buffer now tracks CONFIG_SYS_CBSIZE.

Signed-off-by: John Schmoller <jschmoller@xes-inc.com>

common/main.c

@@ -526,7 +526,7 @@ void reset_cmd_timeout(void)
 
 #define CTL_CH(c)		((c) - 'a' + 1)
 
-#define MAX_CMDBUF_SIZE		256
+#define MAX_CMDBUF_SIZE		CONFIG_SYS_CBSIZE
 
 #define CTL_BACKSPACE		('\b')
 #define DEL			((char)255)