drm/i915: Make addressing mode bits in context descriptor configurable

drm/i915: Make addressing mode bits in context descriptor configurable

Currently the addressing mode bit in context descriptor is statically
generated from the configuration of system-wide PPGTT usage model.

GVT-g will load the PPGTT shadow page table by itself and probably one
guest is using a different addressing mode with i915 host. The addressing
mode bits of a LRC context should be configurable under this case.

v10:

- Fix the identation. (Joonas)

v9:
- Rename the data member in struct i915_gem_context. (Chris)

v8:
- Rename the data member in struct i915_gem_context. (Chris)

v7:
- Move context addressing mode bit into i915_reg.h. (Joonas/Chris)
- Add prefix "INTEL_" for related definitions. (Joonas)

v6:
- Directly save the addressing mode bits inside i915_gem_context. (Chris)
- Move the LRC context addressing mode bits into intel_lrc.h. (Chris)

v5:
- Change USES_FULL_48BIT(dev) to USES_FULL_48BIT(dev_priv) (Tvrtko)

Reviewed-by: Joonas Lahtinen <[email protected]> (v9)
Cc: Joonas Lahtinen <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Signed-off-by: Zhi Wang <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]