ARM: debug: add UART early console support for MSTAR SoCs

This adds the debug_ll uart for the PM UART found on armv7-based MStar
SoCs.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
Acked-by: Daniel Palmer <daniel@thingy.jp>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Mohammed Billoo <mohammed.billoo@gmail.com>
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Signed-off-by: Olof Johansson <olof@lixom.net>