build: Set UHD driver as default configuration

Currently the default configuration is to not build the full
transceiver, which is pointless. Set the UHD driver, which
includes either Ettus or Fairwaves variants, as the default.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
diff --git a/configure.ac b/configure.ac
index 2bfe825..848f887 100644
--- a/configure.ac
+++ b/configure.ac
@@ -63,11 +63,6 @@
         [enable USRP1 gnuradio based transceiver])
 ])
 
-AC_ARG_WITH(uhd, [
-    AS_HELP_STRING([--with-uhd],
-        [enable UHD based transceiver])
-])
-
 AC_ARG_WITH(singledb, [
     AS_HELP_STRING([--with-singledb],
         [enable single daughterboard use on USRP1])
@@ -75,24 +70,22 @@
 
 AS_IF([test "x$with_usrp1" = "xyes"], [
     PKG_CHECK_MODULES(USRP, usrp >= 3.3)
-    # Find and define supported SIMD extensions
-    AX_EXT
 ])
 
-AS_IF([test "x$with_uhd" = "xyes"],[
+AS_IF([test "x$with_usrp1" != "xyes"],[
     PKG_CHECK_MODULES(UHD, uhd >= 003.004.000)
     AC_DEFINE(USE_UHD, 1, Define to 1 if using UHD)
-    AX_EXT
 ])
 
 AS_IF([test "x$with_singledb" = "xyes"], [
     AC_DEFINE(SINGLEDB, 1, Define to 1 for single daughterboard)
 ])
 
-AM_CONDITIONAL(UHD, [test "x$with_uhd" = "xyes"])
+# Find and define supported SIMD extensions
+AX_EXT
+
 AM_CONDITIONAL(USRP1, [test "x$with_usrp1" = "xyes"])
 
-# Defines LIBUSB_TRANSFER_CANCELLED, LIBUSB_TRANSFER_COMPLETED, LIBUSB_SUCCESS, LIBUSB_ERROR_*
 PKG_CHECK_MODULES(LIBUSB, libusb-1.0)
 
 dnl Output files