ubi: Remove flash selection parameter (nor|nand|onenand) from "ubi part"

This patch removes the now unnecessary flash type parameter from the
"ubi part" command. Currently the user has to define the type of flash
he will be using UBI on. Example:

=> ubi part nor partition1

With this patch this type parameter is not needed anymore. The user can
now select the partition directly without the flash type paramter.
Example:

=> ubi part partition1

This breaks backward compatibility right now because of the change in the
command syntax. But UBI support is still quite fresh and the advantage of
this new command is syntax big enough for this change. Additionally the
code is much cleaner now.

Signed-off-by: Stefan Roese <sr@denx.de>
CC: Kyungmin Park <kyungmin.park@samsung.com>