serial/sifive: select SERIAL_EARLYCON

The sifive serial driver implements earlycon support, but unless
another driver is built in that supports earlycon support it won't
be usable. Explicitly select SERIAL_EARLYCON instead.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Paul Walmsley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/Kconfig

···
 	bool "Console on SiFive UART"
 	depends on SERIAL_SIFIVE=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 	help
 	  Select this option if you would like to use a SiFive UART as the
 	  system console.