spi: pl022: Simplify platdata code

pl022 spi driver support both OF_CONTROL and PLATDATA, this
patch is trying to simplify the code that differentiating
platdata vs of_control.
- Move OF_CONTROL code at one place
- Handle clock setup code directly in pl022_spi_ofdata_to_platdata

Acked-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>