serial: msm_geni_serial: Fix the race between termios and ISR

This patch makes sure to process the RX EOT bit post cancel command
as part of stop rx sequencer. There could be a race between ISR and
userspace thread doing stop rx where ISR clears out the interrupts
generated as part of other operations and EOT poll may timeout.

Also there are chances that stop_rx can generate an interrupt if the
peer device sends data when client hasn't disabled the flow control.
This will trigger a call to handle_dma_rx which basically un-maps the
rx dma buffer, handles the rx data and remaps the same rx dma buffer.

As part of baud change, make sure ISR gets called exclusively against
the start_rx call. There is a slight window where dma_map of start_rx
sets the iova as DMA_ERROR_CODE for a while before actually mapping
to valid dma address and ISR uses this invalid address as part of
un-mapping the same buffer address which results into the page fault.

Change-Id: I9c69f7f9399aac060188ccee5648b8b7c46a656b
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>