Move GPIO class to common library

It will soon by used by the power supply code as
well as the power sequencer code, so moving it to
a common location.

Change-Id: Ia3e2bcf27239c6861fcb6a9d45ae08a4eed778b7
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/Makefile.am b/Makefile.am
index ff49c2a..fd4cd96 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -13,6 +13,7 @@
 	$(PHOSPHOR_DBUS_INTERFACES_CFLAGS)
 
 libpower_la_SOURCES = \
+	gpio.cpp \
 	pmbus.cpp \
 	timer.cpp \
 	utility.cpp \