configure: Autodetect VA-API

This fixes a regression (reproducible since 1.2) and restores the
behaviour of 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 1.0 and 1.1.

configure

@@ -142,7 +142,7 @@ Component options:
 
 Hardware accelerators:
   --disable-dxva2          disable DXVA2 code [autodetect]
-  --enable-vaapi           enable VAAPI code
+  --disable-vaapi          disable VAAPI code [autodetect]
   --enable-vda             enable VDA code
   --disable-vdpau          disable VDPAU code [autodetect]
 
@@ -2253,8 +2253,8 @@ enable safe_bitstream_reader
 enable static
 enable swscale_alpha
 
-# By default, enable only those hwaccels that have no external dependencies.
-enable dxva2 vdpau
+# Enable hwaccels by default.
+enable dxva2 vaapi vdpau
 
 # build settings
 SHFLAGS='-shared -Wl,-soname,$$(@F)'
@@ -3987,7 +3987,6 @@ enabled MemoryBarrier && enable atomics_win32
 
 check_lib math.h sin -lm && LIBM="-lm"
 disabled crystalhd || check_lib libcrystalhd/libcrystalhd_if.h DtsCrystalHDVersion -lcrystalhd || disable crystalhd
-enabled vaapi && require vaapi va/va.h vaInitialize -lva
 
 atan2f_args=2
 ldexpf_args=2
@@ -4167,12 +4166,9 @@ require X11 X11/Xlib.h XOpenDisplay -lX11                 &&
 require Xext X11/extensions/XShm.h XShmCreateImage -lXext &&
 require Xfixes X11/extensions/Xfixes.h XFixesGetCursorImage -lXfixes
 
-if ! disabled vaapi; then
-    check_lib va/va.h vaInitialize -lva && {
-        check_cpp_condition va/va_version.h "VA_CHECK_VERSION(0,32,0)" ||
-        warn "Please upgrade to VA-API >= 0.32 if you would like full VA-API support.";
-    } || disable vaapi
-fi
+enabled vaapi &&
+    check_lib va/va.h vaInitialize -lva ||
+    disable vaapi
 
 enabled vdpau &&
     check_cpp_condition vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP" ||