drm/i915: move and rename i915_runtime_pm

Asserts aside, all the code working on this structure is in
intel_runtime_pm.c and uses the intel_ prefix, so move the
structure to intel_runtime_pm.h and adopt the same prefix.

Since all the asserts are now working on the runtime_pm structure,
bring them across as well.

v2: drop unneeded include (Chris), don't rename debugfs, rebase

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613232156.34940-5-daniele.ceraolospurio@intel.com