configure: Default-enable virtual pnor

I'm tired of the lack of CI coverage, and I have to care about it.

Rework the README to reflect the change in default behaviour.

Change-Id: I883be8bc4e89b755185f9f84f0ebd46a05fee71f
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/configure.ac b/configure.ac
index af13732..a6b1453 100644
--- a/configure.ac
+++ b/configure.ac
@@ -47,9 +47,9 @@
 )
 
 AC_ARG_ENABLE([virtual-pnor],
-    AS_HELP_STRING([--enable-virtual-pnor], [Turn on virtual pnor])
+    AS_HELP_STRING([--disable-virtual-pnor], [Turn off virtual pnor support])
 )
-AS_IF([test "x$enable_virtual_pnor" == "xyes"],
+AS_IF([test "x$enable_virtual_pnor" != "xno"],
     [
         PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus])
         PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging])