clk: fractional-divider: add CLK_FRAC_DIVIDER_ZERO_BASED flag support

Adding CLK_FRAC_DIVIDER_ZERO_BASED flag to indicate the numerator and
denominator value in register are start from 0.

This can be used to support frac dividers like below:
Divider output clock = Divider input clock x [(frac +1) / (div +1)]
where frac/div in register is:
000b - Divide by 1.
001b - Divide by 2.
010b - Divide by 3.

Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>