msm_serial_hs: Donot register UART device as PM runtime active

Currently UART device is being registered as PM runtime active
in probe() and set as suspended in shutdown(). With this UART
driver PM runtime suspend is being called when system suspend
is invoked and while resuming from the same which invokes UART
driver LPM functionality. It causes UART communication to stop
if both UART Tx and RX FIFO are empty.

This change donot register UART device as PM runtime active
device as UART driver doesn't use PM runtime APIs for its LPM
functionality.

CRs-Fixed: 479966
Change-Id: I33d0c95e4227fdb1b7d6d514498e161e6e4df465
Signed-off-by: Mayank Rana <mrana@codeaurora.org>