drm/i915: Modify reset func to handle per engine resets

In full gpu reset we prime all engines and reset domains corresponding to
each engine. Per engine reset is just a special case of this process
wherein only a single engine is reset. This change is aimed to modify
relevant functions to achieve this. There are some other steps we carry out
in case of engine reset which are addressed in later patches.

Reset func now accepts a mask of all engines that need to be reset. Where
per engine resets are supported, error handler populates the mask
accordingly otherwise all engines are specified.

v2: ALL_ENGINES mask fixup, better for_each_ring_masked (Chris)
v3: Whitespace fixes (Chris)
v4: Rebase due to s/ring/engine

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458143640-20563-1-git-send-email-mika.kuoppala@intel.com