riscv: select DMA_DIRECT_OPS instead of redefining it

DMA_DIRECT_OPS is defined in lib/Kconfig, so don't duplicate it in
arch/riscv/Kconfig.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/Kconfig

@@ -11,6 +11,7 @@ config RISCV
 	select ARCH_WANT_FRAME_POINTERS
 	select CLONE_BACKWARDS
 	select COMMON_CLK
+	select DMA_DIRECT_OPS
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_CPU_DEVICES
 	select GENERIC_IRQ_SHOW
@@ -89,9 +90,6 @@ config PGTABLE_LEVELS
 config HAVE_KPROBES
 	def_bool n
 
-config DMA_DIRECT_OPS
-	def_bool y
-
 menu "Platform type"
 
 choice