clk: microchip: enable the MPFS clk driver by default if SOC_MICROCHIP_POLARFIRE

clk: microchip: enable the MPFS clk driver by default if SOC_MICROCHIP_POLARFIRE

With the intent of removing driver selects from Kconfig.socs in
arch/riscv, essential drivers that were being selected there could
instead by enabled by defaulting them to the value of the SoC's Kconfig
symbol.

Do so here & drop the depend on RISC-V - the SOC_ symbols are only
defined there anyway.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221123161921.81195-1-conor@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>