Extend init/init_hw split to context init.
   - Move context initialisation in to i915_gem_init_hw
   - Move one off initialisation for render ring to
        i915_gem_validate_context
   - Move default context initialisation to logical_ring_init

Rename intel_lr_context_deferred_create to
intel_lr_context_deferred_alloc, to reflect reduced functionality &
alloc/init split.

This patch is intended to split out the allocation of resources &
initialisation to allow easier reuse of code for resume/gpu reset.

v2: Removed function ptr wrapping of do_switch_context (Daniel Vetter)
    Left ->init_context int intel_lr_context_deferred_alloc
    (Daniel Vetter)
    Remove unnecessary init flag & ring type test. (Daniel Vetter)
    Improve commit message (Daniel Vetter)
v3: On init/reinit, set the hw next sequence number to the sw next
    sequence number. This is set to 1 at driver load time. This prevents
    the seqno being reset on reinit (Chris Wilson)
v4: Set seqno back to ~0 - 0x1000 at start-of-day, and increment by 0x100
    on reset.
    This makes it obvious which bbs are which after a reset. (David Gordon
    & John Harrison)
    Rebase.
v5: Rebase. Fixed rebase breakage. Put context pinning in separate
    function. Removed code churn. (Thomas Daniel)
v6: Cleanup up issues introduced in v2 & v5 (Thomas Daniel)

Issue: VIZ-4798
Signed-off-by: Nick Hoath <nicholas.hoath@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: John Harrison <john.c.harrison@intel.com>
Cc: David Gordon <david.s.gordon@intel.com>
Cc: Thomas Daniel <thomas.daniel@intel.com>
Reviewed-by: Thomas Daniel <thomas.daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>