serial: 8250_omap: Remove rx_dma_broken flag

8250 UART DMA support was marked broken by default as it was not
possible to pause ongoing RX DMA transfer. Now that both SDMA and
EDMA can support pause operation for RX DMA transactions, don't set
rx_dma_broken to true by default. With this patch 8250_omap driver will
use DMA by default.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>