dma/Kconfig: TI_EDMA needs to be boolean

Fix:

arch/arm/common/built-in.o: undefined reference to `edma_filter_fn'

seen with "make ARCH=arm allmodconfig"

Commit 6cba4355 (ARM: edma: Add DT and runtime PM support to the private EDMA
API) adds a dependency on edma_filter_fn() into arch/arm/common/edma.c. Since
this file is always built into the kernel, edma_filter_fn() must be built into
the kernel as well.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>