hvc: haven: Update driver initialization to support console

Console initialization may send data to driver during call to
hvc_instantiate. Thus, these data structures must be initialized before
this call. Reorganize driver initialization to meet this requirement and
improve comments and error handling during initialization.

Change-Id: Ia7b9bc9e2244516d86695839830ff4a16863342a
Signed-off-by: Elliot Berman <eberman@codeaurora.org>