msm: clock-gcc-8974: Support the USB UTMI clock source divider

The gcc_usb30_mock_utmi_clk also contains a CDIV divider
that can do integer division on 8974V2 and newer targets.
Support this divider in clock-gcc-8974.

Drivers will need to set a rate on usb30_utmi_clk_src, and
then set a divider on gcc_usb30_mock_utmi_clk. Both of these
operations shall make use of the clk_set_rate API.

Also update the frequency table on usb30_utmi_clk_src to
include a new 48MHz rate.

Change-Id: I0952fc25b187456eeb98b8bc4a3c5d51fd10a67a
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>