[ARM] pxa/zeus: Allow usage of 8250-compatible UART in uncompress

Zeus console port is wired to a 8250-compatible device (pxa UARTs are
reserved to other uses). This patch allows such a configuration in the
uncompress sequence.

Signed-off-by: Marc Zyngier <maz@misterjones.org>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>