asm-generic: Add dma-contiguous.h

This header is used by arm64 and x86 individually.

Adding to asm-generic to avoid further code repetition while adding cma
to mips.
Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: catalin.marinas@arm.com
Cc: will.deacon@arm.com
Cc: tglx@linutronix.de
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: arnd@arndb.de
Cc: gregkh@linuxfoundation.org
Cc: m.szyprowski@samsung.com
Cc: x86@kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-arch@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7357/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-generic/dma-contiguous.h

+#ifndef _ASM_GENERIC_DMA_CONTIGUOUS_H
+#define _ASM_GENERIC_DMA_CONTIGUOUS_H
+
+#include <linux/types.h>
+
+static inline void
+dma_contiguous_early_fixup(phys_addr_t base, unsigned long size) { }
+
+#endif