gallium/ilo: cleanup intel_winsys.h

gallium/ilo: cleanup intel_winsys.h

Make the header location, inclusion and contents more common with
its i915,r* and nouveau counterparts:

 - Move the header within drivers/ilo.
 - Separate out intel_winsys_create_for_fd into 'drm_public' header.
 - Cleanup the compiler includes.

v2: Move the header to drivers/ilo. Suggested by Chia-I.
v3: Correct intel_winsys.h inclusion. Spotted by Chia-I.

Cc: Chia-I Wu <olvaffe@gmail.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>