clk: x86: Support RV architecture

There is minor difference between previous family of SoC and
the current one. Which is the there is only 48Mh fixed clk.
There is no mux and no option to select another freq as there in previous.

Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>