configs/qemu_sh4-r2d: restore the old sh-sci driver behaviour

configs/qemu_sh4-r2d: restore the old sh-sci driver behaviour

This reverts commit 18e8cf159177100e69d528293f8cf6875c0b1bca (kernel)

The last Qemu kernel update [1] introduced a regresion in sh4 SCIF
serial device. Some keyboard presses are very slow to be taken into
account, perhaps not even taken into account at all. This would
explain why our test infrastructure doesn’t manage to login as root
[2][3][4].

git bisect reported a kernel patch from 4.11, increasing RX FIFO
trigger defaults value for sh-sci (H)SCIF. The kernel patch itself
looks good but the Qemu emulation is not ready to handle this new
setting.

>From Qemu (2.12.0): target/sh4/README.sh4
"Configuration of the second serial port (SCIF) is supported. FIFO
handling infrastructure has been started but is not completed yet."

We can't use the first serial port (ttySC0) because it's the second
SH UART that's emulated by Qemu.

In order to be able to test sh4 architecture with newer kernel,
revert to the old behaviour.

[1] 03fb00f2175cdb4565e26fcb9b3da1c1059de1bd
[2] https://gitlab.com/free-electrons/toolchains-builder/-/jobs/72006425
[3] https://gitlab.com/free-electrons/toolchains-builder/-/jobs/72006427
[4] https://gitlab.com/free-electrons/toolchains-builder/-/jobs/72006426

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>