aspeed/smc: Add DMA calibration settings

When doing calibration, the SPI clock rate in the CE0 Control Register
and the read delay cycles in the Read Timing Compensation Register are
set using bit[11:4] of the DMA Control Register.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190904070506.1052-7-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>