clk: ingenic: Add support for divider tables

Some clocks provided on Ingenic SoCs have dividers, whose hardware value
as written in the register cannot be expressed as an affine function
to the actual divider value.

For instance, for the CPU clock on the JZ4770, the dividers are coded as
follows:

    ------------------
    | Bits     | Div |
    ------------------
    | 0  0  0  |  1  |
    | 0  0  1  |  2  |
    | 0  1  0  |  3  |
    | 0  1  1  |  4  |
    | 1  0  0  |  6  |
    | 1  0  1  |  8  |
    | 1  1  0  | 12  |
    ------------------

To support this setup, we introduce a new field in the
ingenic_cgu_div_info structure that allows to specify the divider table.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>