clk: fractional-divider: tests: Add test suite for edge cases

In light of the recent discovery that the fractional divisor
approximation does not utilize the full available range for clocks that
are flagged CLK_FRAC_DIVIDER_ZERO_BASED [1], implement tests for the
edge cases of this clock type.

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Link: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev [1]
Link: https://lore.kernel.org/r/20230617131041.18313-3-frank@oltmanns.dev
[sboyd@kernel.org: Rename suite and tests slightly, drop unused
includes, store parent rate to compare instead of repeating equation]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>