Blackfin arch: Convert Blackfin GPIO driver to use common gpiolib/gpiochip infrastructure

 - This patch adds support for ARCH_WANT_OPTIONAL_GPIOLIB.
 - It may be changed in future to ARCH_REQUIRE_GPIOLIB.
 - Change GPIO_BANK_NUM use DIV_ROUND_UP( , ) macro

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig
index 19b43f3..004c06c 100644
--- a/arch/blackfin/Kconfig
+++ b/arch/blackfin/Kconfig
@@ -26,6 +26,7 @@
 	default y
 	select HAVE_IDE
 	select HAVE_OPROFILE
+	select ARCH_WANT_OPTIONAL_GPIOLIB
 
 config ZONE_DMA
 	bool