ata: at91: use syscon to configure the smc

Use syscon/regmap to configure the smc. This allows to avoid using
at91sam9_smc.h and to compile the driver in a multiplatform configuration.

The driver will still not probe until the proper DT bindings are added. That
binding will include an atmel,smc property that is a phandle to the SMC the CF
controller is connected to.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>