Revert "serial: pl011: use DMA RX polling by default"

This reverts commit 17438217 on request
of Linus Walleij:
	Greg can you please drop or revert
	commit 17438217
	"serial: pl011: use DMA RX polling by default"
	from the TTY tree until this has been sorted out?

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>