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/README.md b/README.md
index af37bb9..7e00cb8 100644
--- a/README.md
+++ b/README.md
@@ -15,11 +15,10 @@
 The build system is a standard autotools setup. `bootstrap.sh` runs all the
 jobs necessary to initialise autotools.
 
-By default the build is configured and built _without_ the 'virtual PNOR'
+By default the build is configured and built _with_ the 'virtual PNOR'
 feature discussed below. The virtual PNOR functionality is written in C++, and
 due to some autotools clunkiness even if it is disabled mboxd will still be
-linked with `CXX`. Point `CXX` to `cc` at configure time if you do not have a
-C++ compiler for your target (`./configure CXX=cc`).
+linked with `CXX`.
 
 If you are hacking on the reference implementation it's recommended to run
 `bootstrap.sh` with the `dev` argument:
@@ -43,14 +42,15 @@
 $ make check
 ```
 
-In addition to its role as a flash abstraction `mboxd` can also serve as a
-partition/filesystem abstraction. This feature is known as 'virtual PNOR' and
-it can be enabled at `configure` time (note that this requires a C++ compiler
-for your target):
+Through the virtual PNOR feature the daemon's role as a flash abstraction can
+be augmented to support partition/filesystem abstraction. This is complex and
+unnecessary for a number of platforms, and so the feature can be disabled at
+`configure` time. If you do not have a C++ compiler for your target, set
+`CXX=cc`.
 
 ```
 $ ./bootstrap.sh
-$ ./configure --enable-virtual-pnor
+$ ./configure CXX=cc --disable-virtual-pnor
 $ make
 $ make check
 ```
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])