UPSTREAM: lib: rational: copy the rational fraction lib routines from Linux

Copy the best rational approximation calculation routines from Linux.
Typical usecase for these routines is to calculate t

UPSTREAM: lib: rational: copy the rational fraction lib routines from Linux

Copy the best rational approximation calculation routines from Linux.
Typical usecase for these routines is to calculate the M/N divider
values for PLLs to reach a specific clock rate.

This is based on linux kernel commit:
"lib/math/rational.c: fix possible incorrect result from rational
fractions helper"
(sha1: 323dd2c3ed0641f49e89b4e420f9eef5d3d5a881)

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Tero Kristo <kristo@kernel.org>
(cherry picked from commit 7d0f3fbb93cfebd7b5dc5635166e48ab998c4f82)
Change-Id: Ia0b04dcde2e0ed208ae10f2f3ed8648564bd5220
Signed-off-by: Wyon Bi <bivvy.bi@rock-chips.com>

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