mali: ux500: reworked gpu scaling driver

thanks @1N4148
https://github.com/1N4148/s3mini/commit/6df5c6828fe8aabe93548c2283d4f54c02bf33bc

Signed-off-by: Shilin Victor <chrono.monochrome@gmail.com>
PLLDDR: stability fix

Signed-off-by: Shilin Victor <chrono.monochrome@gmail.com>