serial: sh-sci: Submit RX DMA from RX interrupt on (H)SCIF

For DMA receive requests, the driver is only notified by DMA completion
after the whole DMA request has been transferred.  If less data is
received, it will stay stuck until more data arrives.  The driver
handles this by setting up a timer handler from the receive interrupt,
after reception of the first character.

Unlike SCIFA and SCIFB, SCIF and HSCIF don't issue receive interrupts on
reception of individual characters if a receive DMA request is in
progress, so the timer is never set up.

To fix receive DMA on SCIF and HSCIF, submit the receive DMA request
from the receive interrupt handler instead.
In some sense this is similar to the SCIFA/SCIFB behavior, where the
RDRQE (Rx Data Transfer Request Enable) bit is also set from the receive
interrupt handler.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>