Fix CONFIG_TXK_SEL support in the CMake build.

CONFIG_TXK_SEL requires CONFIG_LV_MAP. Warn when not enabled, and
enable it. This matches the configure build.

BUG=aomedia:683

Change-Id: Iba0340d13fcb3cb0d20fc36df6b3def2fc1d92fd

build/cmake/aom_configure.cmake

@@ -277,6 +277,12 @@ if (CONFIG_GPROF)
   require_compiler_flag("-pg" YES)
 endif ()
 
+if (CONFIG_TXK_SEL)
+  if (NOT CONFIG_LV_MAP)
+    change_config_and_warn(CONFIG_LV_MAP 1 CONFIG_TXK_SEL)
+  endif ()
+endif ()
+
 if (CONFIG_WARPED_MOTION)
   if (CONFIG_NCOBMC)
     change_config_and_warn(CONFIG_NCOBMC 0 CONFIG_WARPED_MOTION)