ARM: keystone: config: fix build warning when CONFIG_DMADEVICES is not set

Drop automatic selection of TI_EDMA from Keystone Kconfig file,
as it produces build warning in case if CONFIG_DMADEVICES is not set:

warning: (ARCH_KEYSTONE) selects TI_EDMA which has unmet direct dependencies (DMADEVICES && (ARCH_DAVINCI || ARCH_OMAP || ARCH_KEYSTONE))

Instead enable TI EDMA support from defconfig.

Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Olof Johansson <olof@lixom.net>