ARM: zynq: add support for ARCH_MULTIPLATFORM

The majority of changes are necessary to remove dependencies on header
files within arch/arm/mach-zynq/include/mach:

  uncompress.h
    - Deleted. It is unused for ARCH_MULTIPLATFORM builds.

  uart.h:
    - Move uart definitions out of uart.h into debug/zynq.S, which is
      now the only user

  zynq_soc.h:
    - Move SCU address definitions into common.c.
    - Other #defines, such as PERIPHERAL_CLOCK_RATE, TTC0_BASE, etc, are
      unused and can be dropped

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>