gpio: Drop TZ1090 drivers

Now that arch/metag/ has been removed, along with TZ1090 SoC support,
remove the TZ1090 GPIO drivers. They are of no value without the
architecture and SoC platform code.

Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: linux-gpio@vger.kernel.org
Cc: linux-metag@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>