CLK: clk-twl6040: Initial clock driver for OMAP4+ McPDM fclk clock

On OMAP4+ platforms the functional clock for the McPDM IP is suplied by
the twl6040 codec (bit clock on the PDM bus).
This common clock driver for twl6040 will register the mcpdm_fclk clock to
be used by the McPDM driver to make sure that the needed clocks are
available when needed.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>