stm32f205_timer: Update based on mailling list

Also incldes some of thw PWM work

Signed-off-by: Alistair Francis <alistair23@gmail.com>
stm32f205_syscfg: Update based on mailing list comments

Signed-off-by: Alistair Francis <alistair23@gmail.com>
stm32f205_usart: Update based on mailing list feedback

Signed-off-by: Alistair Francis <alistair23@gmail.com>