gpu: get up to 1k DMA mappings and make it only a warning if it's more than one

4 jobs for feature/hls-rtds2gpu in 1 minute and 13 seconds (queued for 1 second)
Name Stage Failure
build:source Build
/builds/acs/public/villas/VILLASfpga/tests/rtds2gpu.cpp:37:10: fatal error: villas/gpu.hpp: No such file or directory
#include <villas/gpu.hpp>
compilation terminated.
make[2]: *** [tests/CMakeFiles/unit-tests.dir/build.make:207: tests/CMakeFiles/unit-tests.dir/rtds2gpu.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:199: tests/CMakeFiles/unit-tests.dir/all] Error 2
make: *** [Makefile:152: all] Error 2
ERROR: Job failed: exit code 1