axxiaarm: change value of AXXIA_DEBUG_UART_VIRT

The macro AXXIA_DEBUG_UART_VIRT is defined to be 0xf0080000 which
is not in vmalloc zone (0xf0800000-0xff800000), and it will trigger
warning as below:

BUG: mapping for 0x2010080000 at 0xf0080000 out of vmalloc space

So change the value to be 0xf0880000 to avoid this warning.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>