tty: serial: samsung: Declare earlycon for Exynos850

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 <semen.protsenko@linaro.org>
Link: https://patch.msgid.link/20251118024822.28148-1-semen.protsenko@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>