Rename qemu_semihosting_connect_chardevs to
qemu_semihosting_chardev_init; pass the result
directly to qemu_semihosting_console_init.

Store the chardev in SemihostingConsole instead
of SemihostingConfig, which lets us drop
semihosting_get_chardev.

Reviewed-by: Luc Michel <lmichel@kalray.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>