rockchip: rk3368: spl: mark SPL and TPL as supported for ROCKCHIP_RK3368

With SPL and TPL support for the RK3368 in place, mark SPL and TPL as
supported from Kconfig for the RK3368.  As this is primarily tested on
the RK3368-uQ7, we'll leave it to board's individual defconfig to
enable.

Also enable DEBUG_UART_BOARD_INIT for the RK3368, so we get output
during the early boot-up, as we turn on TPL and SPL.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>