spi: aspeed: Support customized decoded address ranges

If "decoded-ranges" is defined in the device tree, the
driver will apply the decoded address ranges from this
property to the controller during probe stage.

This patch refers to the following OpenBMC u-boot patch.
https://patchwork.ozlabs.org/project/openbmc/list/?series=306969



Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>