sh: don't allow non-coherent DMA for NOMMU

The code handling non-coherent DMA depends on being able to remap code
as non-cached.  But that can't be done without an MMU, so using this
option on NOMMU builds is broken.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/Kconfig

@@ -61,6 +61,7 @@ config SUPERH
 	select MAY_HAVE_SPARSE_IRQ
 	select MODULES_USE_ELF_RELA
 	select NEED_SG_DMA_LENGTH
+	select NO_DMA if !MMU && !DMA_COHERENT
 	select NO_GENERIC_PCI_IOPORT_MAP if PCI
 	select OLD_SIGACTION
 	select OLD_SIGSUSPEND
@@ -135,7 +136,7 @@ config DMA_COHERENT
 	bool
 
 config DMA_NONCOHERENT
-	def_bool !DMA_COHERENT
+	def_bool !NO_DMA && !DMA_COHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 
 config PGTABLE_LEVELS