Macros are not suitably namespaced

[bmerry]

Including <gdrapi.h> defines some macros that aren't prefixed with GDR and hence could easily conflict. In particular, MAJOR_VERSION_SHIFT has a high chance of meaning other things in other places (a Github search shows 200 places, although mostly it's copies of tegra_platform.c/h). GPU_PAGE_* are slightly better but still not really unique to gdrcopy.

[drossetti]

@pakmarkthub can you scope the necessary work?