ARC: [arcfpga] RIP early uart platform device stuff

With ARC uart driver switching to generic earlycon, we no longer need
this ugliness. You won't be missed.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>