configs: rockchip: drop useless DEBUG_UART_SKIP_INIT

configs: rockchip: drop useless DEBUG_UART_SKIP_INIT

DEBUG_UART_SKIP_INIT feature is implemented only by s5p (DEBUG_UART_S5P)
and pl01x (DEBUG_UART_PL010 or DEBUG_UART_PL011) serial drivers, but all
ARCH_ROCKCHIP configs rely on default DEBUG_UART_NS16550. The ns16550
serial driver does not depends on DEBUG_UART_SKIP_INIT, so drop it from
rockchip configs.

Signed-off-by: Massimo Pegorer <massimo.pegorer@vimar.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>