MIPS: drop selected EARLY_PRINTK configs for MACH_REALTEK_RTL

MACH_REALTEK_RTL declares that the system supports early printk , but
this is not actually implemented as intended. The system is left with a
non-functional early0 console because the setup_8250_early_printk_port()
call provided for MIPS_GENERIC is never used to set this up. Generic
ns16550a earlycon works, so devices should use that for early output.
This means that SYS_HAS_EARLY_PRINTK and USE_GENERIC_EARLY_PRINTK_8250
do not need to be selected.

Additionally, as reported by Lukas Bulwahn, the selected symbol
SYS_HAS_EARLY_PRINTK_8250 does not actually exist, so should also be
dropped.

Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Bert Vermeulen <bert@biot.com>
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>