configure: move x264_csp_bgr check under general libx264 checks

This makes the libx264rgb check work when pkg-config is utilized
and x264.h is not part of the standard include path (as is often
with cross-compilation, or when you just have a custom prefix in
general in f.ex. your home directory).

The X264_BUILD >= 118 required by configure since 2011 should have
X264_CSP_BGR defined unconditionally (it was added a few X264_BUILD
updates earlier), but as 134cba728b
added this additional check, I have kept it for now.

configure

@@ -6132,7 +6132,6 @@ check_builtin MemoryBarrier windows.h "MemoryBarrier()"
 check_builtin sync_val_compare_and_swap "" "int *ptr; int oldval, newval; __sync_val_compare_and_swap(ptr, oldval, newval)"
 check_builtin gmtime_r time.h "time_t *time; struct tm *tm; gmtime_r(time, tm)"
 check_builtin localtime_r time.h "time_t *time; struct tm *tm; localtime_r(time, tm)"
-check_builtin x264_csp_bgr "stdint.h x264.h" "X264_CSP_BGR"
 
 case "$custom_allocator" in
     jemalloc)
@@ -6530,6 +6529,7 @@ enabled libx264           && { check_pkg_config libx264 x264 "stdint.h x264.h" x
                                { require libx264 "stdint.h x264.h" x264_encoder_encode "-lx264 $pthreads_extralibs $libm_extralibs" &&
                                  warn "using libx264 without pkg-config"; } } &&
                              require_cpp_condition libx264 x264.h "X264_BUILD >= 118" &&
+                             check_cpp_condition x264_csp_bgr x264.h "X264_CSP_BGR" &&
                              check_cpp_condition libx262 x264.h "X264_MPEG2"
 enabled libx265           && require_pkg_config libx265 x265 x265.h x265_api_get &&
                              require_cpp_condition libx265 x265.h "X265_BUILD >= 70"