MIPS: Alchemy: Determine cohereny at runtime based on cpu type

All Alchemy chips have coherent DMA, but for example the USB or AC97
peripherals on the Au1000/1500/1100 are not.
This patch uses DMA_MAYBE_COHERENT on Alchemy and sets coherentio based
on CPU type.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/6576/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index daef670..51f5a09 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -63,6 +63,7 @@
 	select CEVT_R4K
 	select CSRC_R4K
 	select IRQ_CPU
+	select DMA_MAYBE_COHERENT	# Au1000,1500,1100 aren't, rest is
 	select SYS_HAS_CPU_MIPS32_R1
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_APM_EMULATION