obmc-phosphor-image: devtools refactoring

Move i2c tools to the devtools package, right next to gpio tools.

Rename extrasdevtools to just devtools.  "Extra" doesn't convey any
useful information.  We can get away with this rename since noone is
touching the package.

Add an IMAGE_FEATURE for devtools, for easy opt-out.

Change-Id: I92d24a415f071e9828f1badfa2327870d7db494a
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/recipes-phosphor/images/obmc-phosphor-image.bb b/recipes-phosphor/images/obmc-phosphor-image.bb
index a0c14ff..c12b188 100644
--- a/recipes-phosphor/images/obmc-phosphor-image.bb
+++ b/recipes-phosphor/images/obmc-phosphor-image.bb
@@ -8,6 +8,7 @@
         obmc-bmc-state-mgmt \
         obmc-chassis-mgmt \
         obmc-chassis-state-mgmt \
+        obmc-devtools \
         obmc-fan-control \
         obmc-fan-mgmt \
         obmc-flash-mgmt \