tty: serial: samsung: Declare earlycon for Exynos850

It makes it possible to use just "earlycon" param in kernel cmdline
on Exynos850 based boards instead of "earlycon=exynos4210,0x13820000",
as described in [1]:

When used with no options, the early console is determined by
stdout-path property in device tree's chosen node

[1] Documentation/admin-guide/kernel-parameters.txt

Signed-off-by: Sam Protsenko <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/samsung_tty.c

···
 			s5pv210_early_console_setup);
 OF_EARLYCON_DECLARE(artpec8, "axis,artpec8-uart",
 			s5pv210_early_console_setup);
+OF_EARLYCON_DECLARE(exynos850, "samsung,exynos850-uart",
+			s5pv210_early_console_setup);
 
 static int __init gs101_early_console_setup(struct earlycon_device *device,
 					    const char *opt)