rockchip: Move to MULTI_CONSOLE_API

rockchip: Move to MULTI_CONSOLE_API

This patch changes all Rockchip platforms to use the new
MULTI_CONSOLE_API. The platform-specific plat_crash_console
implementations are removed so that the platform can use the ones from
the common platform code instead.

Also change the registers used in plat_crash_print_regs. The existing
use of x16 and x17 has always been illegal, since those registers are
reserved for use by the linker as a temporary scratch registers in
intra-procedure-call veneers and can never be expected to maintain their
values across a function call.

Change-Id: I8249424150be8d5543ed4af93b56756795a5288f
Signed-off-by: Julius Werner <jwerner@chromium.org>