drm/hdcp: optimizing the srm handling

As we are not using the sysfs infrastructure anymore, link to it is
removed. And global srm data and mutex to protect it are removed,
with required handling at revocation check function.

v2:
  srm_data is dropped and few more comments are addressed.
v3:
  ptr passing around is fixed with functional testing.
v4:
  fix htmldoc [lkp]

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Suggested-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212102942.26568-2-ramalingam.c@intel.com