soc: qcom: ipc_router_mhi_xprt: Do not defer MHI open and close work

MHI change requires all work to be finished before returning from
the ERROR, SHUTDOWN and DISABLE callbacks. Call mhi xprt enable and
disable functions directly instead of deferring the work. Remove
calls to mhi_close_channel to prevent calling MHI after the disable
callback.

CRs-Fixed: 1095436
Change-Id: I37910cfd3b51693b1f3bc84815d95595602690e8
Signed-off-by: Chris Lew <clew@codeaurora.org>