dt-bindings: net: c_can: Update binding for clock and power-domains property

CAN driver uses the clk_get_rate call to determine the frequency of the
functional clock. OMAP based SoCs do not require the clock property since
hwmod already handles creating a "fck" clock thats accessible to drivers.
However, this isn't the case for 66AK2G which makes the clocks property
require for that SoC.

66AK2G requires a new property. Therefore, update the binding to also make
this property requirement clear. Also clarify that for OMAP based SoCs
ti,hwmod is a required property.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>