clk: vc5: Add support for IDT VersaClock 5P49V6901

Update IDT VersaClock 5 driver to support IDT VersaClock 6 5P49V6901.
This chip has two clock inputs (external XTAL or external CLKIN), four
fractional dividers (FODs) and five clock outputs (four universal clock
outputs and one reference clock output at OUT0_SELB_I2C).

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Alexey Firago <alexey_firago@mentor.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: linux-renesas-soc@vger.kernel.org
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
on Salvator-XS with the display LVDS output.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>