target/openrisc: Remove duplicate features property

target/openrisc: Remove duplicate features property

The features property has stored the exact same thing as the cpucfgr
spr. Remove the feature enum and property as it is not needed.

In order to preserve the behavior or keeping features accross reset this
patch moves cpucfgr into the non reset region of the state struct.  Since
the cpucfgr is read only this means we only need to sset cpucfgr once
during class init.

Signed-off-by: Stafford Horne <shorne@gmail.com>