clk: COMMON_CLK_RPMI should depend on RISCV

clk: COMMON_CLK_RPMI should depend on RISCV

The RISC-V platform management interface (RPMI) is only available on
RISC-V platforms.  Hence add a dependency on RISCV, to prevent asking
the user about this driver when configuring a kernel for a different
architecture.

Fixes: 5ba9f520f41a33c9 ("clk: Add clock driver for the RISC-V RPMI clock service group")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Paul Walmsley <pjw@kernel.org>