ARM: zynq: Enable big-endian

Enable ARCH_SUPPORTS_BIG_ENDIAN in Kconfig.

zynq_secondary_trampoline is the first function
that is called on secondary CPU.
Reference:
"ARM: mcpm: fix big endian issue in mcpm startup code"
(sha1: 519ceb9f)

Fix early printk support. Based on:
"ARM: pl01x debug code endian fix"
(sha1: 76e3faf1)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>