Blackfin: import gpio/portmux layer from Linux

The current pinmux handling has spread throughout Blackfin drivers and
board code and is getting hideous to maintain.  So import the gpio and
portmux layer from the Blackfin Linux code.  This should spur a serious
of cleanups across the Blackfin tree.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/include/asm/system.h b/arch/blackfin/include/asm/system.h
index 6bc7208..952438e 100644
--- a/arch/blackfin/include/asm/system.h
+++ b/arch/blackfin/include/asm/system.h
@@ -118,4 +118,6 @@
 	return tmp;
 }
 
+void bfin_reset_boot_spi_cs(unsigned short pin);
+
 #endif	/* _BLACKFIN_SYSTEM_H */