wspoon: Inhibit mrw fan-control fan config

Use a hardcoded config file for the Witherspoon fan presence
configuration.

Hopefully a somewhat temporary workaround of missing tags in the
Witherspoon MRW.

Change-Id: I28525d69ac340371b96d09390c7f2800d89fca5c
diff --git a/meta-witherspoon/recipes-phosphor/fans/phosphor-fan-control-fan-config%.bbappend b/meta-witherspoon/recipes-phosphor/fans/phosphor-fan-control-fan-config%.bbappend
new file mode 100644
index 0000000..72d991c
--- /dev/null
+++ b/meta-witherspoon/recipes-phosphor/fans/phosphor-fan-control-fan-config%.bbappend
@@ -0,0 +1 @@
+FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"