meta-ibm: set OBMC_ORG_YAML_SUBDIRS in machines

The OBMC_ORG_YAML_SUBDIRS variable is intended to be set system-wide
and not via bbappends.  There was an existing 'ibm-distrovars.inc'
that was unused.  Rename it as appropriate, add it to the machines,
and remove the bbappend files.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id5acd359f41c17ec9e68d1f0717e2f5c1bf96dcf
diff --git a/meta-ibm/conf/machine/witherspoon-tacoma.conf b/meta-ibm/conf/machine/witherspoon-tacoma.conf
index 8d2a907..9826d55 100644
--- a/meta-ibm/conf/machine/witherspoon-tacoma.conf
+++ b/meta-ibm/conf/machine/witherspoon-tacoma.conf
@@ -10,6 +10,7 @@
 require conf/machine/include/obmc-bsp-common.inc
 require conf/machine/include/openpower.inc
 require conf/machine/include/p9.inc
+require conf/distro/include/ibm-yaml.inc
 require conf/distro/include/openpower-virtual-pnor.inc
 require conf/distro/include/phosphor-mmc.inc
 require conf/distro/include/ibm-mpreboot.inc