qemu: don't use C functions for the crash console callbacks

Use the console_pl011_core_* functions directly in the crash console
callbacks.

This bypasses the MULTI_CONSOLE_API for the crash console (UART1), but
allows using the crash console before the C runtime has been initialized
(eg to call ASM_ASSERT). This retains backwards compatibility with respect
to functionality when the old API is used.

Use the MULTI_CONSOLE_API to register UART0 as the boot and runtime
console.

Fixes ARM-software/tf-issues#572

Signed-off-by: Michalis Pappas <mpappas@fastmail.fm>