qemu_sh4_r2d: update to fix serial console support

sh4-r2d has a serial port, however it's the second SH UART that's
emulated by Qemu so we need to adjust the kernel configuration for it to
see the relevant UART and adjust the qemu command line for it too.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>