Revert "MIPS: Don't unnecessarily include kmalloc.h into <asm/cache.h>."

Commit 296e46db ("MIPS: Don't unnecessarily include kmalloc.h into
<asm/cache.h>.") claimed that the inclusion of the machine's kmalloc.h
from asm/cache.h is unnecessary, but this is not true.

Without including kmalloc.h we don't get a definition for
ARCH_DMA_MINALIGN, which means we no longer suitably align DMA. Further
to this the definition of ARCH_KMALLOC_MINALIGN provided by linux/slab.h
ends up being set to the alignment of an unsigned long long value rather
than to ARCH_DMA_MINALIGN, which means that buffers allocated using
kmalloc may no longer be safely aligned for use with DMA.

Fix this by re-adding the include of kmalloc.h in asm/cache.h. This
reverts commit 296e46db ("MIPS: Don't unnecessarily include
kmalloc.h into <asm/cache.h>.")
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: 296e46db ("MIPS: Don't unnecessarily include kmalloc.h into <asm/cache.h>.")
Cc: linux-mips@linux-mips.org
Cc: stable <stable@vger.kernel.org> # v4.12+
Patchwork: https://patchwork.linux-mips.org/patch/16895/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/cache.h

@@ -9,6 +9,8 @@
 #ifndef _ASM_CACHE_H
 #define _ASM_CACHE_H
 
+#include <kmalloc.h>
+
 #define L1_CACHE_SHIFT		CONFIG_MIPS_L1_CACHE_SHIFT
 #define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)