Revert "omap: serial: disable serial port irq during suspend"

This reverts commit 0af4d0c479b8ec6d9b8bc329b193a07331672fea.

This might be the cause for the sporadic loss of connection to
the modem, as motorola also changed this driver and these irq-
changes do not touch the motorola additions.

Change-Id: I23d0ccf01017a50d6dac592207e747e127b839f1