drm/i915/selftests: huge page tests

drm/i915/selftests: huge page tests

v2: mock test page support configurations and add MI_STORE_DWORD test

v3: run all mockable huge page tests on all platforms via the mock_device

v4: add pin_update regression test
    various improvements suggested by Chris

v5: fix issues reported by kbuild
    test single sg spanning multiple page sizes
    don't explode when running the live-tests through the appgtt

v6: lots of improvements from Chris

v7: run on each engine for igt_write_huge
    add simple tmpfs fallback test

v8: size_t is bad
    don't break the i386 build

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006145041.21673-18-matthew.auld@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006221833.32439-17-chris@chris-wilson.co.uk