feat(intel): add macro to switch between different UART PORT

HSD #1509626040:
This patch is to add the flexibility for BL2 and BL31
to choose different UART output port at platform_def.h
using parameter PLAT_INTEL_UART_BASE

This patch also fixing the plat_helpers.S where the
UART BASE is hardcoded to PLAT_UART0_BASE. It is then

Signed-off-by: Boon Khai Ng <boon.khai.ng@intel.com>
Change-Id: Iccfa7ec64e4955b531905778be4da803045d3c8f
7 files changed