target-openrisc: Drop OpenRISCCPUList

It was missed in 92a3136174f60ee45b113296cb2c2a5225b00369 (cpu:
Introduce CPUListState struct) because its naming did not match the
*CPUListState pattern. Use the generalized CPUListState instead.

Signed-off-by: Andreas Färber <afaerber@suse.de>