gpio: generalize for all generic gpio providers

The Blackfin gpio command isn't terribly Blackfin-specific.  So generalize
the few pieces into two new optional helpers:
	name_to_gpio() - turn a string name into a GPIO #
	gpio_status() - display current pin bindings (think /proc/gpio)

Once these pieces are pulled out, we can relocate the cmd_gpio.c into the
common directory.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/common/Makefile b/common/Makefile
index 26380c6..432a9de 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -98,6 +98,7 @@
 ifdef CONFIG_FPGA
 COBJS-$(CONFIG_CMD_FPGA) += cmd_fpga.o
 endif
+COBJS-$(CONFIG_CMD_GPIO) += cmd_gpio.o
 COBJS-$(CONFIG_CMD_I2C) += cmd_i2c.o
 COBJS-$(CONFIG_CMD_IDE) += cmd_ide.o
 COBJS-$(CONFIG_CMD_IMMAP) += cmd_immap.o