This patch introduces the 'plat_enable_console' handler to allow
the platform to enable the right console. Tegra194 platform supports
multiple console, while all the previous platforms support only one
console.

For Tegra194 platforms, the previous bootloader checks the platform
config and sets the uart-id boot parameter, to 0xFE. On seeing this
boot parameter, the platform port uses the proper memory aperture
base address to communicate with the SPE. This functionality is
currently protected by a platform macro, ENABLE_CONSOLE_SPE.

Change-Id: I3972aa376d66bd10d868495f561dc08fe32fcb10
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>