MIPS: mm: XBurst CPU requires sync after DMA

I am not sure why this is required, but if this is not enabled, reading
from a buffer in which data has been DMA'd may read incorrect values.

This used to happen for instance in mmc_app_send_scr()
(drivers/mmc/core/sd_ops.c), where data is DMA'd to a buffer then copied
by the CPU to a different location.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/Kconfig

@@ -112,6 +112,7 @@ config MACH_INGENIC
 	select SYS_SUPPORTS_LITTLE_ENDIAN
 	select SYS_SUPPORTS_ZBOOT
 	select DMA_NONCOHERENT
+	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select IRQ_MIPS_CPU
 	select PINCTRL
 	select GPIOLIB

arch/mips/mm/dma-noncoherent.c

@@ -32,6 +32,7 @@ static inline bool cpu_needs_post_dma_flush(void)
 	case CPU_R12000:
 	case CPU_BMIPS5000:
 	case CPU_LOONGSON2EF:
+	case CPU_XBURST:
 		return true;
 	default:
 		/*