cpufreq: remove unicore32 driver

The unicore32 port is removed from the kernel.
There is no point to keep stale cpufreq driver for this architecture.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>