gpio/mvebu-gpio: Make mvebu-gpio depend on OF_CONFIG

When building without device tree support (for the mv78x00 SoCs for
example), the build failed because of_irq_count is undeclared. However
mvebu-gpio is not designed to build without device tree support. So
make it depends on OF_CONFIG, remove the #ifdef OF_CONFIG line and the
platform_device_id.

Tested on RD-78x00-mASA, DB-78460-BP, DB-88F6710-BP-DDR3,
DB-MV784MP-GP, Mirabox and OpenBlocks AX3.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 8ae1f5b..682de75 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -172,6 +172,7 @@
 config GPIO_MVEBU
 	def_bool y
 	depends on PLAT_ORION
+	depends on OF
 	select GPIO_GENERIC
 	select GENERIC_IRQ_CHIP