drm/i915/hdcp: read RxInfo once when reading RepeaterAuth_Send_ReceiverID_List

When reading RepeaterAuth_Send_ReceiverID_List, RxInfo is read by itself
once to retrieve the DEVICE_COUNT to calculate the size of the
ReceiverID list then read a second time as a part of reading ReceiverID
list.

On some MST docking stations, RxInfo can only be read after the RxStatus
READY bit is set otherwise the read will return -EIO. The spec states that
the READY bit should be cleared as soon as RxInfo has been read.

In this case, the first RxInfo read succeeds but after the READY bit is
cleared, the second read fails.

Fix it by reading RxInfo once and storing it before reading the rest of
RepeaterAuth_Send_ReceiverID_List once we know the size.

Modify get_receiver_id_list_size() to read and store RxInfo in the
message buffer and also parse DEVICE_COUNT so we know the size of
RepeaterAuth_Send_ReceiverID_List.

Afterwards, retrieve the rest of the message at the offset for
seq_num_V.

Changes in v5:
- Don't change the offset define for Send_ReceiverID_List
  When reading, update message offset to account for RxInfo being read

Changes in v4:
- rebase and edit commit message

Changes in v3:
- remove comment

Changes in v2:
- remove unnecessary moving of drm_i915_private from patch 1

Signed-off-by: Juston Li <juston.li@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Tested-by: Suraj K <suraj.kandpal@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210819184835.1181323-3-juston.li@intel.com