ARM: zynq: Fix uart0 early console virtual address

Virtual address have to have the same offset within
a 2MB aligned section of virtual/phycial address space.

Fix uart0 virtual address to be align with physical one.
Also remove UART_SIZE which is completely unused.

Reported-by: Russ Smith <russells@google.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>