meta-openpower: Define i2c-occ feature

OpenPOWER P8 systems uses i2c to access occ.
Define i2c-occ OBMC_MACHINE_FEATURES and append EXTRA_OECONF in
openpower-occ-control.bb so that it compiles with I2C OCC support.

Enabled this feature on Palmetto first.

Change-Id: I1c07d28494fc5e87e86a3be1bfcfd955770e14e7
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/meta-palmetto/conf/machine/palmetto.conf b/meta-palmetto/conf/machine/palmetto.conf
index 1fedc69..5d71bf4 100644
--- a/meta-palmetto/conf/machine/palmetto.conf
+++ b/meta-palmetto/conf/machine/palmetto.conf
@@ -4,6 +4,7 @@
 require conf/machine/include/ast2400.inc
 require conf/machine/include/obmc-bsp-common.inc
 require conf/machine/include/ibm.inc
+require conf/machine/include/p8.inc
 
 UBOOT_MACHINE_palmetto = "ast_g4_ncsi_config"
 UBOOT_ENTRYPOINT = "0x40008000"