cpuidle: mvebu: Fix the name of the states

The length name of the states 2 was too long to fit in the allocated
string (limited to 16 bytes). This lead to improper string displayed
through sysfs.

This patch shorten the name by removing the reference to Marvell and
to the CPU as both are implicit. For coherency the same change have
been done for the states 1.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>