Revert "serial: 8250: dma: Allow driver operations before starting DMA transfers"

This reverts commit ad7fd9f6 which is
commit e4fb03fe upstream.

It breaks the Android GKI kernel abi, and is not needed for Android
devices, so revert it for now.  If it is needed for this branch, it can
come back later in an ABI-stable way.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Id5501ecc2d1bdb34c06ab436f7a9d0dd9537b7e2