ARM: S3C24XX: Add missing DMACH_DT_PROP

Commit 2b908075 (spi: s3c64xx: add device tree support) requires
the DMACH_DT_PROP element in the dma_ch enum. It's not used on non-DT
platforms but has to be present nevertheless.

So mimic the dummy-add of DMACH_DT_PROP on s3c64xx for s3c24xx
machines, to correct the build breakage for the s3c24xx variants
using the s3c64xx-spi-driver.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>