msm: mdm: cleanup the way the external modem is shutdown and reset

The platform device for the data peripheral between the apq
and the external modem should be removed before asserting
the reset line that will power down the modem. This was
causing a crash when the phone was powered down normally.

Also, put back the delay during which we check for the
mdm2ap_status gpio going low before asserting the reset line.

Change-Id: Ic32425ab84f944f51b4cc906ff4f242899859b31
Signed-off-by: Joel King <joelking@codeaurora.org>