net: qrtr: haven: Rearrange init order

Doorbells can be received immediately after registering. Ensure the
qrtr endpoint has been registered and initialized before enabling the
rx doorbell.

The tx doorbell should be done before registering the endpoint since
the qrtr core logic can attempt to send immediately after registration.

Change-Id: Ice332b4a053ea6e78bfded1e3625d8c527917e7b
Signed-off-by: Chris Lew <clew@codeaurora.org>