intel: adapt intel_winsys for our needs

No mutex.  Always associate a intel_winsys with a hardware context.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3945440..4d9341f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,6 +22,10 @@
 if (NOT LIBDRM_FOUND)
 	message(FATAL_ERROR "libdrm not found")
 endif()
+pkg_check_modules(LIBDRM_INTEL REQUIRED libdrm_intel)
+if (NOT LIBDRM_INTEL_FOUND)
+	message(FATAL_ERROR "libdrm not found")
+endif()
 
 if (CMAKE_COMPILER_IS_GNUCC)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 -Werror -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter")