Add support for PCA953x I2C gpio devices

Initial support for NXP's 4 and 8 bit I2C gpio expanders
(eg pca9537, pca9557, etc). The CONFIG_PCA953X define
enables support for the devices while the CONFIG_CMD_PCA953X
define enables the pca953x command. The CONFIG_CMD_PCA953X_INFO
define enables an 'info' sub-command which provides summary
information for the given pca953x device.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/Makefile b/Makefile
index 4df4812..0fc6490 100644
--- a/Makefile
+++ b/Makefile
@@ -228,6 +228,7 @@
 LIBS += drivers/block/libblock.a
 LIBS += drivers/dma/libdma.a
 LIBS += drivers/fpga/libfpga.a
+LIBS += drivers/gpio/libgpio.a
 LIBS += drivers/hwmon/libhwmon.a
 LIBS += drivers/i2c/libi2c.a
 LIBS += drivers/input/libinput.a
@@ -407,6 +408,7 @@
 TAG_SUBDIRS += common
 TAG_SUBDIRS += drivers/bios_emulator
 TAG_SUBDIRS += drivers/block
+TAG_SUBDIRS += drivers/gpio
 TAG_SUBDIRS += drivers/hwmon
 TAG_SUBDIRS += drivers/i2c
 TAG_SUBDIRS += drivers/input