aspeed/smc: Fix DMA support for AST2600

aspeed/smc: Fix DMA support for AST2600

Recent firmwares uses SPI DMA transfers in U-Boot to load the
different images (kernel, initrd, dtb) in the SoC DRAM. The AST2600
FMC model is missing the masks to be applied on the DMA registers
which resulted in incorrect values. Fix that and wire the SPI
controllers which have DMA support on the AST2600.

Fixes: bcaa8ddd081c ("aspeed/smc: Add AST2600 support")
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Message-id: 20200320053923.20565-1-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>