sw:drv: wait for DDR calibration with timeout

In the following commit we have added a 1ms delay before checking the
DDR calibration status. We thought it to be enough, but it is not. On
some designs the calibration takes more time.

commit 2647a65e ("sw:drv: add delay before checking DDR status")

This patch polls for the DDR calibration status and waits until it is
complete or the timeout expires. The timeout is set to 1s, if it happens
it is really a bad sign, and it should not be considered acceptable.

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>