prime_mmap_kms: show case dma-buf new API and processes restrictions

dma-buf new API consists of:

- mmap(dma_buf_fd, ...): the ability to map a dma-buf file-descriptor of a
graphics buffer to the userspace, and more importantly, to actually write on
the mapped pointer (which was not possible before). It’s worth noting that the
Direct Rendering Manager (DRM) and the hardware driver implementation are
fundamentally important to safely export the graphics handle to be mapped.

- ioctl(dma_buf_fd, DMA_BUF_IOCTL_SYNC, &args): cache coherency management in
cases where the CPU and GPU devices are being accessed through dma-buf at the
same time. Coherency markers, which forward directly to existing dma-buf
device drivers vfunc hooks, are exposed to the userspace through the
DMA_BUF_IOCTL_SYNC ioctl and have to be used before and after the mapped area
is accessed. This is fundamentally important in hardware architectures where
the graphics engine and the CPU cores don't share caches but also important in
other type of hardware where the memory hierarchy is (most of the time)
coherent. More details can be found in this patch set:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c11e391da2a8fe973c3c2398452000bed505851e

v2: use uint32_t for color type, increment the variable and add
--interactive-debug=paint
v3: use igt_display_commit() to mode set the crtc so the rectangle is shown
painted; also added Testcase description on the beginning of the file.
v4: remove crtc actually which seems superfluous; add a igt_skip_on in case
support for dma-buf mmap is nonexistent.

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
Signed-off-by: Marius Vlad <marius.c.vlad@intel.com>

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