tools include: Add an initial math64.h

Add an initial math64.h similar to linux/math64.h with functions
mul_u64_u64_div64() and mul_u64_u32_shr(). This isn't a direct copy of
include/linux/math64.h as that doesn't define mul_u64_u64_div64().

Implementation was written by Peter Zilkstra based on linux/math64.h
and div64.h[1]. The original implementation was not optimal on arm64 as
__int128 division is not optimal with a call out to __udivti3, so I
dropped the __int128 variant of mul_u64_u64_div64().

[1] https://lore.kernel.org/lkml/[email protected]/

Signed-off-by: Rob Herring <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Itaru Kitayama <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Will Deacon <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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