MIPS: BMIPS: Delete unused Kconfig symbol

MIPS: BMIPS: Delete unused Kconfig symbol

This was left over from an earlier iteration of the BMIPS irqchip changes.
It doesn't actually have an effect, so let's nuke it.

Reported-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Kevin Cernekee <cernekee@chromium.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: stable@vger.kernel.org # v4.1+
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9910/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>