MIPS: MSP71xx: Remove gpio drivers

The PMC MSP71XX gpio drivers were added in v2.6.28, see commit
9fa32c6b02 ("MIPS: PMC MSP71XX gpio drivers"). They are only built if
CONFIG_HAVE_GPIO_LIB is set.

But the Kconfig symbol HAVE_GPIO_LIB was already removed in v2.6.27, see
commit 7444a72eff ("gpiolib: allow user-selection"). So these drivers
were never buildable. Perhaps no-one noticed because there are no in
tree users of msp71xx_init_gpio() and msp71xx_init_gpio_extended().
Anyhow, these drivers can safely be removed.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/5345/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>