rpmsg: qcom_glink_bgcom: Correct the remote intent ack sequence

Correct the wait logic for remote intent ack sequence to make
glink wait for both remote intent ack and actual intent allocation.
This is needed as bg sends intent ack first and then sends actual
intent. If waiting for actual intent is not there, glink might
end up sending intent request again. Correct the size of message
in send_data API as the current size is 6 words but, BG expects
either 4 words or 8 words only.

Change-Id: I3e90efd296ac9134160ea2db6749161c4963d78e
Signed-off-by: Prudhvi Yarlagadda <pyarlaga@codeaurora.org>