gd: fix --with-freetype option

* 'yes' value means using pkg-config to find freetype, other values are using
  FREETYPE_CONFIG=/bin/freetype-config and freetype-config isn't
  in STAGING_LIBDIR but in STAGING_BINDIR/crossscripts/freetype-config

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>