MIPS: R6: Fix PREF instruction usage by memcpy for MIPS R6

Disable usage of PREF instruction usage by memcpy for MIPS R6.

MIPS R6 redefines PREF instruction with smaller offset than
ordinary MIPS. However, the memcpy code uses PREF instruction
with offsets bigger than +-256 bytes.

Malta kernels already disable usage of PREF for memcpy.

This was found during adaptation of MIPS R6 for virtual board
used by Android emulator.
Signed-off-by: NLeonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: NMiodrag Dinic <miodrag.dinic@imgtec.com>
Signed-off-by: NGoran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: NAleksandar Markovic <aleksandar.markovic@imgtech.com>
Cc: James.Hogan@imgtec.com
Cc: Paul.Burton@imgtec.com
Cc: Raghu.Gandham@imgtec.com
Cc: Leonid.Yegoshin@imgtec.com
Cc: Douglas.Leung@imgtec.com
Cc: Petar.Jovanovic@imgtec.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16510/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/lib/memcpy.S

@@ -28,6 +28,9 @@
 #ifdef CONFIG_MIPS_MALTA
 #undef CONFIG_CPU_HAS_PREFETCH
 #endif
+#ifdef CONFIG_CPU_MIPSR6
+#undef CONFIG_CPU_HAS_PREFETCH
+#endif
 
 #include <asm/asm.h>
 #include <asm/asm-offsets.h>