microblaze: remove check for CONFIG_XILINX_CONSOLE

There's been a check for CONFIG_XILINX_CONSOLE since v2.6.30. But the
Kconfig symbol XILINX_CONSOLE was never added. Remove this check.

And, since DUMMY_CONSOLE depends on VT, we can now drop the check for
CONFIG_VT.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>