RISC-V: stop selecting SiFive clock and serial drivers directly

The SiFive clock and serial drivers will now default to the value of
SOC_SIFIVE so there is no need to directly select their symbols
anymore.
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/riscv/Kconfig.socs

@@ -18,10 +18,6 @@ config ARCH_SIFIVE
 
 config SOC_SIFIVE
 	bool "SiFive SoCs"
-	select SERIAL_SIFIVE if TTY
-	select SERIAL_SIFIVE_CONSOLE if TTY
-	select CLK_SIFIVE
-	select CLK_SIFIVE_PRCI
 	select ERRATA_SIFIVE if !XIP_KERNEL
 	help
 	  This enables support for SiFive SoC platform hardware.