cmd: mmc: modify more readable about hwpartition usage

cmd: mmc: modify more readable about hwpartition usage

Modified more readable about hwpartition usage.
Because it's difficult to understand how to use its command.
The arguments didn't optional.
mmc hwpartition needs to pass <USER> <GP> <MODE> as arguments.
Description about each arguments what is required is the below:
 USER - <user> <enh> <start> <cnt> <wrrel> <{on|off}>
 GP   - <{gp1|gp2|gp3|gp4}> <cnt> <enh> <wrrel> <{on|off}>
 MODE - <{check|set|complete}>

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>