drm/i915: Fix sha_text population code

This patch fixes a few bugs:

1- We weren't taking into account sha_leftovers when adding multiple
   ksvs to sha_text. As such, we were or'ing the end of ksv[j - 1] with
   the beginning of ksv[j]

2- In the sha_leftovers == 2 and sha_leftovers == 3 case, bstatus was
   being placed on the wrong half of sha_text, overlapping the leftover
   ksv value

3- In the sha_leftovers == 2 case, we need to manually terminate the
   byte stream with 0x80 since the hardware doesn't have enough room to
   add it after writing M0

The upside is that all of the HDCP supported HDMI repeaters I could
find on Amazon just strip HDCP anyways, so it turns out to be _really_
hard to hit any of these cases without an MST hub, which is not (yet)
supported. Oh, and the sha_leftovers == 1 case works perfectly!

Fixes: ee5e5e7a ("drm/i915: Add HDCP framework + base implementation")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.17+
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203173638.94919-2-sean@poorly.run #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20191212190230.188505-2-sean@poorly.run #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20200117193103.156821-2-sean@poorly.run #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20200218220242.107265-2-sean@poorly.run #v4
Link: https://patchwork.freedesktop.org/patch/msgid/20200305201236.152307-2-sean@poorly.run #v5
Link: https://patchwork.freedesktop.org/patch/msgid/20200429195502.39919-2-sean@poorly.run #v6
Link: https://patchwork.freedesktop.org/patch/msgid/20200623155907.22961-2-sean@poorly.run

 #v7

Changes in v2:
-None
Changes in v3:
-None
Changes in v4:
-Rebased on intel_de_write changes
Changes in v5:
-None
Changes in v6:
-None
Changes in v7:
-None
Changes in v8:
-None

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200818153910.27894-2-sean@poorly.run