rpmsg: glink: Fix character device allocation

RPMSG devices opened through the control device ioctl inherit the
rpmsg_device from the control device. The control device is not
initialized with a channel for the create_ept function. Initialize a
glink channel for the control device and remove the unneeded
structures for the character control device.

Change-Id: Ib5ce3e2297625d969931d2f166100b3381edbdca
Signed-off-by: Chris Lew <clew@codeaurora.org>